[Kernels] Add Flash Linear Attention Kernels (#24518)

Signed-off-by: youkaichao <youkaichao@gmail.com>

tools/mypy.sh

@@ -29,7 +29,7 @@ run_mypy vllm/engine
 run_mypy vllm/executor
 run_mypy vllm/inputs
 run_mypy vllm/lora
-run_mypy vllm/model_executor
+run_mypy --exclude 'vllm/model_executor/layers/fla/ops' vllm/model_executor
 run_mypy vllm/plugins
 run_mypy vllm/worker
 run_mypy vllm/v1

vllm/model_executor/layers/fla/__init__.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang

vllm/model_executor/layers/fla/ops/__init__.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+from .chunk import chunk_gated_delta_rule
+from .fused_recurrent import fused_recurrent_gated_delta_rule
+from .layernorm_guard import RMSNormGated
+
+__all__ = [
+    "RMSNormGated",
+    "chunk_gated_delta_rule",
+    "fused_recurrent_gated_delta_rule",
+]

vllm/model_executor/layers/fla/ops/chunk.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+# ruff: noqa: E501
+import warnings
+from typing import Optional
+
+import torch
+from einops import rearrange
+
+from .chunk_delta_h import chunk_gated_delta_rule_fwd_h
+from .chunk_o import chunk_fwd_o
+from .chunk_scaled_dot_kkt import chunk_scaled_dot_kkt_fwd
+from .cumsum import chunk_local_cumsum
+from .l2norm import l2norm_fwd
+from .solve_tril import solve_tril
+from .utils import SUPPRESS_LEVEL, input_guard
+from .wy_fast import recompute_w_u_fwd
+
+
+def chunk_gated_delta_rule_fwd(q: torch.Tensor,
+                               k: torch.Tensor,
+                               v: torch.Tensor,
+                               g: torch.Tensor,
+                               beta: torch.Tensor,
+                               scale: float,
+                               initial_state: torch.Tensor,
+                               output_final_state: bool,
+                               cu_seqlens: Optional[torch.LongTensor] = None):
+    g = chunk_local_cumsum(g, chunk_size=64, cu_seqlens=cu_seqlens)
+    # obtain WY representation. u is actually the new v.
+    A = chunk_scaled_dot_kkt_fwd(k=k,
+                                 beta=beta,
+                                 g_cumsum=g,
+                                 cu_seqlens=cu_seqlens,
+                                 output_dtype=torch.float32)
+    A = solve_tril(A=A, cu_seqlens=cu_seqlens, output_dtype=k.dtype)
+    w, u = recompute_w_u_fwd(
+        k=k,
+        v=v,
+        beta=beta,
+        A=A,
+        g_cumsum=g,
+        cu_seqlens=cu_seqlens,
+    )
+    h, v_new, final_state = chunk_gated_delta_rule_fwd_h(
+        k=k,
+        w=w,
+        u=u,
+        g=g,
+        initial_state=initial_state,
+        output_final_state=output_final_state,
+        cu_seqlens=cu_seqlens,
+    )
+    o = chunk_fwd_o(
+        q=q,
+        k=k,
+        v=v_new,
+        h=h,
+        g=g,
+        scale=scale,
+        cu_seqlens=cu_seqlens,
+    )
+    if SUPPRESS_LEVEL < 3:
+        return g, o, A, final_state, None, None, None
+    elif SUPPRESS_LEVEL >= 3:
+        return g, o, A, final_state, w, h, v_new
+
+
+class ChunkGatedDeltaRuleFunction(torch.autograd.Function):
+
+    @staticmethod
+    @input_guard
+    @torch.amp.custom_fwd(device_type='cuda')
+    def forward(ctx,
+                q: torch.Tensor,
+                k: torch.Tensor,
+                v: torch.Tensor,
+                g: torch.Tensor,
+                beta: torch.Tensor,
+                scale: float,
+                initial_state: torch.Tensor,
+                output_final_state: bool,
+                cu_seqlens: Optional[torch.LongTensor] = None,
+                use_qk_l2norm_in_kernel: bool = False):
+        if use_qk_l2norm_in_kernel:
+            q = l2norm_fwd(q)
+            k = l2norm_fwd(k)
+
+        g, o, A, final_state, w, h, v_new = chunk_gated_delta_rule_fwd(
+            q=q,
+            k=k,
+            v=v,
+            g=g,
+            beta=beta,
+            scale=scale,
+            initial_state=initial_state,
+            output_final_state=output_final_state,
+            cu_seqlens=cu_seqlens,
+        )
+        ctx.scale = scale
+        ctx.use_qk_l2norm_in_kernel = use_qk_l2norm_in_kernel
+        return o.to(q.dtype), final_state
+
+
+@torch.compiler.disable
+def chunk_gated_delta_rule(q: torch.Tensor,
+                           k: torch.Tensor,
+                           v: torch.Tensor,
+                           g: torch.Tensor,
+                           beta: torch.Tensor,
+                           scale: float = None,
+                           initial_state: torch.Tensor = None,
+                           output_final_state: bool = False,
+                           cu_seqlens: Optional[torch.LongTensor] = None,
+                           head_first: bool = False,
+                           use_qk_l2norm_in_kernel: bool = False):
+    r"""
+    Args:
+        q (torch.Tensor):
+            queries of shape `[B, T, H, K]` if `head_first=False` else `[B, H, T, K]`.
+        k (torch.Tensor):
+            keys of shape `[B, T, H, K]` if `head_first=False` else `[B, H, T, K]`.
+        v (torch.Tensor):
+            values of shape `[B, T, H, V]` if `head_first=False` else `[B, H, T, V]`.
+        g (torch.Tensor):
+            (forget) gating tensor (in log space!) of shape `[B, T, H]` if `head_first=False` else `[B, H, T]`.
+        beta (torch.Tensor):
+            betas of shape `[B, T, H]` if `head_first=False` else `[B, H, T]`.
+        scale (Optional[int]):
+            Scale factor for the RetNet attention scores.
+            If not provided, it will default to `1 / sqrt(K)`. Default: `None`.
+        initial_state (Optional[torch.Tensor]):
+            Initial state of shape `[N, H, K, V]` for `N` input sequences.
+            For equal-length input sequences, `N` equals the batch size `B`.
+            Default: `None`.
+        output_final_state (Optional[bool]):
+            Whether to output the final state of shape `[N, H, K, V]`. Default: `False`.
+        cu_seqlens (torch.LongTensor):
+            Cumulative sequence lengths of shape `[N+1]` used for variable-length training,
+            consistent with the FlashAttention API.
+        head_first (Optional[bool]):
+            Whether the inputs are in the head-first format, which is not supported for variable-length inputs.
+            Default: `False`.
+
+    Returns:
+        o (torch.Tensor):
+            Outputs of shape `[B, T, H, V]` if `head_first=False` else `[B, H, T, V]`.
+        final_state (torch.Tensor):
+            Final state of shape `[N, H, K, V]` if `output_final_state=True` else `None`.
+
+    Examples::
+        >>> import torch
+        >>> import torch.nn.functional as F
+        >>> from einops import rearrange
+        >>> from fla.ops.gated_delta_rule import chunk_gated_delta_rule
+        # inputs with equal lengths
+        >>> B, T, H, K, V = 4, 2048, 4, 512, 512
+        >>> q = torch.randn(B, T, H, K, dtype=torch.bfloat16, device='cuda')
+        >>> k = F.normalize(torch.randn(B, T, H, K, dtype=torch.bfloat16, device='cuda'), p=2, dim=-1)
+        >>> v = torch.randn(B, T, H, V, dtype=torch.bfloat16, device='cuda')
+        >>> beta = torch.rand(B, T, H, dtype=torch.bfloat16, device='cuda').sigmoid()
+        >>> g = F.logsigmoid(torch.rand(B, T, H, dtype=torch.bfloat16, device='cuda'))
+        >>> h0 = torch.randn(B, H, K, V, dtype=torch.bfloat16, device='cuda')
+        >>> o, ht = chunk_gated_delta_rule(
+            q, k, v, g, beta,
+            initial_state=h0,
+            output_final_state=True
+        )
+        # for variable-length inputs, the batch size `B` is expected to be 1 and `cu_seqlens` is required
+        >>> q, k, v, beta, g = map(lambda x: rearrange(x, 'b t ... -> 1 (b t) ...'), (q, k, v, beta, g))
+        # for a batch with 4 sequences, `cu_seqlens` with 5 start/end positions are expected
+        >>> cu_seqlens = q.new_tensor([0, 2048, 4096, 6144, 8192], dtype=torch.long)
+        >>> o_var, ht_var = chunk_gated_delta_rule(
+            q, k, v, g, beta,
+            initial_state=h0,
+            output_final_state=True,
+            cu_seqlens=cu_seqlens
+        )
+    """
+    assert q.dtype == k.dtype == v.dtype
+    assert q.dtype != torch.float32, "ChunkGatedDeltaRuleFunction does not support float32. Please use bfloat16."
+    assert len(
+        beta.shape
+    ) == 3, "beta must be of shape [B, T, H] if head_first=False, or [B, H, T] otherwise."
+
+    if head_first:
+        raise DeprecationWarning(
+            "head_first is deprecated and will be removed in a future version. "
+            "Please use head_first=False for now instead.",
+            stacklevel=2)
+        q, k, v, beta, g = map(
+            lambda x: rearrange(x, 'b h t ... -> b t h ...'),
+            (q, k, v, beta, g))
+    if not head_first and q.shape[1] < q.shape[2]:
+        warnings.warn(
+            f"Input tensor shape suggests potential format mismatch: seq_len ({q.shape[1]}) < num_heads ({q.shape[2]}). "
+            "This may indicate the inputs were passed in head-first format [B, H, T, ...] "
+            "when head_first=False was specified. "
+            "Please verify your input tensor format matches the expected shape [B, T, H, ...].",
+            stacklevel=2)
+    if cu_seqlens is not None:
+        if q.shape[0] != 1:
+            raise ValueError(
+                f"The batch size is expected to be 1 rather than {q.shape[0]} when using `cu_seqlens`."
+                f"Please flatten variable-length inputs before processing.")
+        if initial_state is not None and initial_state.shape[0] != len(
+                cu_seqlens) - 1:
+            raise ValueError(
+                f"The number of initial states is expected to be equal to the number of input sequences, "
+                f"i.e., {len(cu_seqlens) - 1} rather than {initial_state.shape[0]}."
+            )
+    if scale is None:
+        scale = k.shape[-1]**-0.5
+    o, final_state = ChunkGatedDeltaRuleFunction.apply(
+        q, k, v, g, beta, scale, initial_state, output_final_state, cu_seqlens,
+        use_qk_l2norm_in_kernel)
+    if head_first:
+        o = rearrange(o, 'b t h ... -> b h t ...')
+    return o, final_state

vllm/model_executor/layers/fla/ops/chunk_delta_h.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+# ruff: noqa: E501
+from typing import Optional
+
+import torch
+
+from vllm.triton_utils import tl, triton
+
+from .index import prepare_chunk_indices, prepare_chunk_offsets
+from .op import exp, safe_exp
+from .utils import is_nvidia_hopper, use_cuda_graph
+
+NUM_WARPS = [2, 4] if is_nvidia_hopper else [2, 4, 8, 16]
+
+
+@triton.heuristics({
+    'USE_G': lambda args: args['g'] is not None,
+    'USE_INITIAL_STATE': lambda args: args['h0'] is not None,
+    'STORE_FINAL_STATE': lambda args: args['ht'] is not None,
+    'SAVE_NEW_VALUE': lambda args: args['v_new'] is not None,
+    'IS_VARLEN': lambda args: args['cu_seqlens'] is not None,
+})
+@triton.autotune(
+    configs=[
+        triton.Config({'BV': BV}, num_warps=num_warps, num_stages=num_stages)
+        for num_warps in [2, 4] for num_stages in [2, 3, 4] for BV in [32, 64]
+    ],
+    key=['H', 'K', 'V', 'BT', 'USE_G'],
+    use_cuda_graph=use_cuda_graph,
+)
+@triton.jit(do_not_specialize=['T'])
+def chunk_gated_delta_rule_fwd_kernel_h_blockdim64(
+    k,
+    v,
+    w,
+    v_new,
+    g,
+    h,
+    h0,
+    ht,
+    cu_seqlens,
+    chunk_offsets,
+    T,
+    H: tl.constexpr,
+    Hg: tl.constexpr,
+    K: tl.constexpr,
+    V: tl.constexpr,
+    BT: tl.constexpr,
+    BV: tl.constexpr,
+    USE_G: tl.constexpr,
+    USE_INITIAL_STATE: tl.constexpr,
+    STORE_FINAL_STATE: tl.constexpr,
+    SAVE_NEW_VALUE: tl.constexpr,
+    IS_VARLEN: tl.constexpr,
+):
+    i_v, i_nh = tl.program_id(0), tl.program_id(1)
+    i_n, i_h = i_nh // H, i_nh % H
+    if IS_VARLEN:
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+        NT = tl.cdiv(T, BT)
+        boh = tl.load(chunk_offsets + i_n).to(tl.int32)
+    else:
+        bos, eos = i_n * T, i_n * T + T
+        NT = tl.cdiv(T, BT)
+        boh = i_n * NT
+
+    # [BK, BV]
+    b_h1 = tl.zeros([64, BV], dtype=tl.float32)
+    if K > 64:
+        b_h2 = tl.zeros([64, BV], dtype=tl.float32)
+    if K > 128:
+        b_h3 = tl.zeros([64, BV], dtype=tl.float32)
+    if K > 192:
+        b_h4 = tl.zeros([64, BV], dtype=tl.float32)
+
+    # calculate offset
+    h += (boh * H + i_h) * K * V
+    v += (bos * H + i_h) * V
+    k += (bos * Hg + i_h // (H // Hg)) * K
+    w += (bos * H + i_h) * K
+    if SAVE_NEW_VALUE:
+        v_new += (bos * H + i_h) * V
+    stride_v = H * V
+    stride_h = H * K * V
+    stride_k = Hg * K
+    stride_w = H * K
+    if USE_INITIAL_STATE:
+        h0 = h0 + i_nh * K * V
+    if STORE_FINAL_STATE:
+        ht = ht + i_nh * K * V
+
+    # load initial state
+    if USE_INITIAL_STATE:
+        p_h0_1 = tl.make_block_ptr(h0, (K, V), (V, 1), (0, i_v * BV), (64, BV),
+                                   (1, 0))
+        b_h1 += tl.load(p_h0_1, boundary_check=(0, 1)).to(tl.float32)
+        if K > 64:
+            p_h0_2 = tl.make_block_ptr(h0, (K, V), (V, 1), (64, i_v * BV),
+                                       (64, BV), (1, 0))
+            b_h2 += tl.load(p_h0_2, boundary_check=(0, 1)).to(tl.float32)
+        if K > 128:
+            p_h0_3 = tl.make_block_ptr(h0, (K, V), (V, 1), (128, i_v * BV),
+                                       (64, BV), (1, 0))
+            b_h3 += tl.load(p_h0_3, boundary_check=(0, 1)).to(tl.float32)
+        if K > 192:
+            p_h0_4 = tl.make_block_ptr(h0, (K, V), (V, 1), (192, i_v * BV),
+                                       (64, BV), (1, 0))
+            b_h4 += tl.load(p_h0_4, boundary_check=(0, 1)).to(tl.float32)
+
+    # main recurrence
+    for i_t in range(NT):
+        p_h1 = tl.make_block_ptr(h + i_t * stride_h, (K, V), (V, 1),
+                                 (0, i_v * BV), (64, BV), (1, 0))
+        tl.store(p_h1, b_h1.to(p_h1.dtype.element_ty), boundary_check=(0, 1))
+        if K > 64:
+            p_h2 = tl.make_block_ptr(h + i_t * stride_h, (K, V), (V, 1),
+                                     (64, i_v * BV), (64, BV), (1, 0))
+            tl.store(p_h2,
+                     b_h2.to(p_h2.dtype.element_ty),
+                     boundary_check=(0, 1))
+        if K > 128:
+            p_h3 = tl.make_block_ptr(h + i_t * stride_h, (K, V), (V, 1),
+                                     (128, i_v * BV), (64, BV), (1, 0))
+            tl.store(p_h3,
+                     b_h3.to(p_h3.dtype.element_ty),
+                     boundary_check=(0, 1))
+        if K > 192:
+            p_h4 = tl.make_block_ptr(h + i_t * stride_h, (K, V), (V, 1),
+                                     (192, i_v * BV), (64, BV), (1, 0))
+            tl.store(p_h4,
+                     b_h4.to(p_h4.dtype.element_ty),
+                     boundary_check=(0, 1))
+
+        p_v = tl.make_block_ptr(v, (T, V), (stride_v, 1), (i_t * BT, i_v * BV),
+                                (BT, BV), (1, 0))
+        p_v_new = tl.make_block_ptr(v_new, (T, V), (stride_v, 1),
+                                    (i_t * BT, i_v * BV), (BT, BV),
+                                    (1, 0)) if SAVE_NEW_VALUE else None
+        b_v_new = tl.zeros([BT, BV], dtype=tl.float32)
+        p_w = tl.make_block_ptr(w, (T, K), (stride_w, 1), (i_t * BT, 0),
+                                (BT, 64), (1, 0))
+        b_w = tl.load(p_w, boundary_check=(0, 1))
+        b_v_new += tl.dot(b_w, b_h1.to(b_w.dtype))
+        if K > 64:
+            p_w = tl.make_block_ptr(w, (T, K), (stride_w, 1), (i_t * BT, 64),
+                                    (BT, 64), (1, 0))
+            b_w = tl.load(p_w, boundary_check=(0, 1))
+            b_v_new += tl.dot(b_w, b_h2.to(b_w.dtype))
+        if K > 128:
+            p_w = tl.make_block_ptr(w, (T, K), (stride_w, 1), (i_t * BT, 128),
+                                    (BT, 64), (1, 0))
+            b_w = tl.load(p_w, boundary_check=(0, 1))
+            b_v_new += tl.dot(b_w, b_h3.to(b_w.dtype))
+        if K > 192:
+            p_w = tl.make_block_ptr(w, (T, K), (stride_w, 1), (i_t * BT, 192),
+                                    (BT, 64), (1, 0))
+            b_w = tl.load(p_w, boundary_check=(0, 1))
+            b_v_new += tl.dot(b_w, b_h4.to(b_w.dtype))
+        b_v_new = -b_v_new + tl.load(p_v, boundary_check=(0, 1))
+
+        if SAVE_NEW_VALUE:
+            p_v_new = tl.make_block_ptr(v_new, (T, V), (stride_v, 1),
+                                        (i_t * BT, i_v * BV), (BT, BV), (1, 0))
+            tl.store(p_v_new,
+                     b_v_new.to(p_v_new.dtype.element_ty),
+                     boundary_check=(0, 1))
+
+        if USE_G:
+            last_idx = min((i_t + 1) * BT, T) - 1
+            b_g_last = tl.load(g + bos * H + last_idx * H + i_h)
+            p_g = tl.make_block_ptr(g + bos * H + i_h, (T, ), (H, ),
+                                    (i_t * BT, ), (BT, ), (0, ))
+            b_g = tl.load(p_g, boundary_check=(0, ))
+            b_v_new = b_v_new * safe_exp(b_g_last - b_g)[:, None]
+            b_g_last = exp(b_g_last)
+            b_h1 = b_h1 * b_g_last
+            if K > 64:
+                b_h2 = b_h2 * b_g_last
+            if K > 128:
+                b_h3 = b_h3 * b_g_last
+            if K > 192:
+                b_h4 = b_h4 * b_g_last
+        b_v_new = b_v_new.to(k.dtype.element_ty)
+        p_k = tl.make_block_ptr(k, (K, T), (1, stride_k), (0, i_t * BT),
+                                (64, BT), (0, 1))
+        b_k = tl.load(p_k, boundary_check=(0, 1))
+        b_h1 += tl.dot(b_k, b_v_new)
+        if K > 64:
+            p_k = tl.make_block_ptr(k, (K, T), (1, stride_k), (64, i_t * BT),
+                                    (64, BT), (0, 1))
+            b_k = tl.load(p_k, boundary_check=(0, 1))
+            b_h2 += tl.dot(b_k, b_v_new)
+        if K > 128:
+            p_k = tl.make_block_ptr(k, (K, T), (1, stride_k), (128, i_t * BT),
+                                    (64, BT), (0, 1))
+            b_k = tl.load(p_k, boundary_check=(0, 1))
+            b_h3 += tl.dot(b_k, b_v_new)
+        if K > 192:
+            p_k = tl.make_block_ptr(k, (K, T), (1, stride_k), (192, i_t * BT),
+                                    (64, BT), (0, 1))
+            b_k = tl.load(p_k, boundary_check=(0, 1))
+            b_h4 += tl.dot(b_k, b_v_new)
+
+    # epilogue
+    if STORE_FINAL_STATE:
+        p_ht = tl.make_block_ptr(ht, (K, V), (V, 1), (0, i_v * BV), (64, BV),
+                                 (1, 0))
+        tl.store(p_ht, b_h1.to(p_ht.dtype.element_ty), boundary_check=(0, 1))
+        if K > 64:
+            p_ht = tl.make_block_ptr(ht, (K, V), (V, 1), (64, i_v * BV),
+                                     (64, BV), (1, 0))
+            tl.store(p_ht,
+                     b_h2.to(p_ht.dtype.element_ty),
+                     boundary_check=(0, 1))
+        if K > 128:
+            p_ht = tl.make_block_ptr(ht, (K, V), (V, 1), (128, i_v * BV),
+                                     (64, BV), (1, 0))
+            tl.store(p_ht,
+                     b_h3.to(p_ht.dtype.element_ty),
+                     boundary_check=(0, 1))
+        if K > 192:
+            p_ht = tl.make_block_ptr(ht, (K, V), (V, 1), (192, i_v * BV),
+                                     (64, BV), (1, 0))
+            tl.store(p_ht,
+                     b_h4.to(p_ht.dtype.element_ty),
+                     boundary_check=(0, 1))
+
+
+def chunk_gated_delta_rule_fwd_h(
+    k: torch.Tensor,
+    w: torch.Tensor,
+    u: torch.Tensor,
+    g: Optional[torch.Tensor] = None,
+    initial_state: Optional[torch.Tensor] = None,
+    output_final_state: bool = False,
+    chunk_size: int = 64,  # SY: remove this argument and force chunk size 64?
+    save_new_value: bool = True,
+    cu_seqlens: Optional[torch.LongTensor] = None,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    B, T, Hg, K, V = *k.shape, u.shape[-1]
+    H = u.shape[-2]
+    BT = chunk_size
+
+    chunk_indices = prepare_chunk_indices(
+        cu_seqlens, chunk_size) if cu_seqlens is not None else None
+    # N: the actual number of sequences in the batch with either equal or variable lengths
+    if cu_seqlens is None:
+        N, NT, chunk_offsets = B, triton.cdiv(T, BT), None
+    else:
+        N, NT, chunk_offsets = len(cu_seqlens) - 1, len(
+            chunk_indices), prepare_chunk_offsets(cu_seqlens, BT)
+    assert K <= 256, "current kernel does not support head dimension larger than 256."
+
+    h = k.new_empty(B, NT, H, K, V)
+    final_state = k.new_empty(
+        N, H, K, V, dtype=torch.float32) if output_final_state else None
+
+    v_new = torch.empty_like(u) if save_new_value else None
+
+    def grid(meta):
+        return (triton.cdiv(V, meta['BV']), N * H)
+
+    chunk_gated_delta_rule_fwd_kernel_h_blockdim64[grid](
+        k=k,
+        v=u,
+        w=w,
+        v_new=v_new,
+        g=g,
+        h=h,
+        h0=initial_state,
+        ht=final_state,
+        cu_seqlens=cu_seqlens,
+        chunk_offsets=chunk_offsets,
+        T=T,
+        H=H,
+        Hg=Hg,
+        K=K,
+        V=V,
+        BT=BT)
+    return h, v_new, final_state

vllm/model_executor/layers/fla/ops/chunk_o.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+
+# ruff: noqa: E501
+
+from typing import Optional
+
+import torch
+
+from vllm.triton_utils import tl, triton
+
+from .index import prepare_chunk_indices
+from .op import exp, safe_exp
+from .utils import FLA_GDN_FIX_BT, check_shared_mem, is_nvidia_hopper
+
+BKV_LIST = [64, 128] if check_shared_mem() else [32, 64]
+NUM_WARPS = [2, 4] if is_nvidia_hopper else [2, 4, 8]
+
+
+@triton.heuristics({
+    'USE_G': lambda args: args['g'] is not None,
+    'IS_VARLEN': lambda args: args['cu_seqlens'] is not None
+})
+@triton.autotune(
+    configs=[
+        triton.Config({
+            'BK': BK,
+            'BV': BV
+        },
+                      num_warps=num_warps,
+                      num_stages=num_stages) for BK in BKV_LIST
+        for BV in BKV_LIST for num_warps in NUM_WARPS
+        for num_stages in [2, 3, 4]
+    ],
+    key=['H', 'K', 'V', 'BT'],
+)
+@triton.jit(do_not_specialize=['T'])
+def chunk_fwd_kernel_o(
+    q,
+    k,
+    v,
+    h,
+    g,
+    o,
+    cu_seqlens,
+    chunk_indices,
+    scale,
+    T,
+    H: tl.constexpr,
+    Hg: tl.constexpr,
+    K: tl.constexpr,
+    V: tl.constexpr,
+    BT: tl.constexpr,
+    BK: tl.constexpr,
+    BV: tl.constexpr,
+    USE_G: tl.constexpr,
+    IS_VARLEN: tl.constexpr,
+):
+    i_v, i_t, i_bh = tl.program_id(0), tl.program_id(1), tl.program_id(2)
+    i_b, i_h = i_bh // H, i_bh % H
+
+    if IS_VARLEN:
+        i_tg = i_t
+        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(
+            tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+        NT = tl.cdiv(T, BT)
+    else:
+        NT = tl.cdiv(T, BT)
+        i_tg = i_b * NT + i_t
+        bos, eos = i_b * T, i_b * T + T
+
+    # offset calculation
+    q += (bos * Hg + i_h // (H // Hg)) * K
+    k += (bos * Hg + i_h // (H // Hg)) * K
+    v += (bos * H + i_h) * V
+    o += (bos * H + i_h) * V
+    h += (i_tg * H + i_h).to(tl.int64) * K * V
+
+    b_o = tl.zeros([BT, BV], dtype=tl.float32)
+    b_A = tl.zeros([BT, BT], dtype=tl.float32)
+
+    for i_k in range(tl.cdiv(K, BK)):
+        p_q = tl.make_block_ptr(q, (T, K), (Hg * K, 1), (i_t * BT, i_k * BK),
+                                (BT, BK), (1, 0))
+        p_k = tl.make_block_ptr(k, (K, T), (1, Hg * K), (i_k * BK, i_t * BT),
+                                (BK, BT), (0, 1))
+        p_h = tl.make_block_ptr(h, (K, V), (V, 1), (i_k * BK, i_v * BV),
+                                (BK, BV), (1, 0))
+        # [BT, BK]
+        b_q = tl.load(p_q, boundary_check=(0, 1))
+        # [BK, BT]
+        b_k = tl.load(p_k, boundary_check=(0, 1))
+        # [BK, BV]
+        b_h = tl.load(p_h, boundary_check=(0, 1))
+
+        # [BT, BK] @ [BK, BV] -> [BT, BV]
+        b_o += tl.dot(b_q, b_h)
+        # [BT, BK] @ [BK, BT] -> [BT, BT]
+        b_A += tl.dot(b_q, b_k)
+
+    if USE_G:
+        g += bos * H + i_h
+        p_g = tl.make_block_ptr(g, (T, ), (H, ), (i_t * BT, ), (BT, ), (0, ))
+        b_g = tl.load(p_g, boundary_check=(0, ))
+        b_o = b_o * exp(b_g)[:, None]
+        b_A = b_A * safe_exp(b_g[:, None] - b_g[None, :])
+
+    o_i = tl.arange(0, BT)
+    m_A = o_i[:, None] >= o_i[None, :]
+    b_A = tl.where(m_A, b_A, 0)
+
+    p_v = tl.make_block_ptr(v, (T, V), (H * V, 1), (i_t * BT, i_v * BV),
+                            (BT, BV), (1, 0))
+    p_o = tl.make_block_ptr(o, (T, V), (H * V, 1), (i_t * BT, i_v * BV),
+                            (BT, BV), (1, 0))
+    b_v = tl.load(p_v, boundary_check=(0, 1))
+
+    # to fix mma -> mma layout conversion
+    # already solved by triton v3.2 or higher
+    b_o = b_o * scale + tl.dot(b_A.to(b_v.dtype), b_v) * scale
+    tl.store(p_o, b_o.to(p_o.dtype.element_ty), boundary_check=(0, 1))
+
+
+def chunk_fwd_o(
+        q: torch.Tensor,
+        k: torch.Tensor,
+        v: torch.Tensor,
+        h: torch.Tensor,
+        g: Optional[torch.Tensor] = None,  # cumsum of log decay
+        scale: Optional[float] = None,
+        cu_seqlens: Optional[torch.LongTensor] = None,
+        chunk_size: int = 64) -> torch.Tensor:
+    B, T, Hg, K, V = *q.shape, v.shape[-1]
+    H = v.shape[-2]
+    if FLA_GDN_FIX_BT:
+        BT = 64
+    else:
+        BT = min(chunk_size, max(16, triton.next_power_of_2(T)))
+    chunk_indices = prepare_chunk_indices(
+        cu_seqlens, BT) if cu_seqlens is not None else None
+    NT = triton.cdiv(T, BT) if cu_seqlens is None else len(chunk_indices)
+    if scale is None:
+        scale = k.shape[-1]**-0.5
+
+    o = torch.empty_like(v)
+
+    def grid(meta):
+        return (triton.cdiv(V, meta['BV']), NT, B * H)
+
+    chunk_fwd_kernel_o[grid](
+        q,
+        k,
+        v,
+        h,
+        g,
+        o,
+        cu_seqlens,
+        chunk_indices,
+        scale,
+        T=T,
+        H=H,
+        Hg=Hg,
+        K=K,
+        V=V,
+        BT=BT,
+    )
+    return o

vllm/model_executor/layers/fla/ops/chunk_scaled_dot_kkt.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+# ruff: noqa: E501
+from typing import Optional
+
+import torch
+
+from vllm.triton_utils import tl, triton
+
+from .index import prepare_chunk_indices
+from .op import safe_exp
+
+
+@triton.heuristics({
+    'IS_VARLEN': lambda args: args['cu_seqlens'] is not None,
+    'USE_G': lambda args: args['g_cumsum'] is not None
+})
+@triton.autotune(
+    configs=[
+        triton.Config({'BK': BK}, num_warps=num_warps, num_stages=num_stages)
+        for BK in [32, 64, 128] for num_warps in [2, 4, 8]
+        for num_stages in [2, 3, 4]
+    ],
+    key=['H', 'K', 'BT', 'IS_VARLEN'],
+)
+@triton.jit(do_not_specialize=['T'])
+def chunk_scaled_dot_kkt_fwd_kernel(
+    k,
+    beta,
+    g_cumsum,
+    A,
+    cu_seqlens,
+    chunk_indices,
+    T,
+    H: tl.constexpr,
+    Hg: tl.constexpr,
+    K: tl.constexpr,
+    BT: tl.constexpr,
+    BK: tl.constexpr,
+    IS_VARLEN: tl.constexpr,
+    USE_G: tl.constexpr,
+):
+    i_t, i_bh = tl.program_id(0), tl.program_id(1)
+    i_b, i_h = i_bh // H, i_bh % H
+    if IS_VARLEN:
+        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(
+            tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+    else:
+        bos, eos = i_b * T, i_b * T + T
+    o_t = tl.arange(0, BT)
+
+    p_beta = tl.make_block_ptr(beta + bos * H + i_h, (T, ), (H, ),
+                               (i_t * BT, ), (BT, ), (0, ))
+    b_beta = tl.load(p_beta, boundary_check=(0, ))
+
+    b_A = tl.zeros([BT, BT], dtype=tl.float32)
+    for i_k in range(tl.cdiv(K, BK)):
+        p_k = tl.make_block_ptr(k + (bos * Hg + i_h // (H // Hg)) * K, (T, K),
+                                (Hg * K, 1), (i_t * BT, i_k * BK), (BT, BK),
+                                (1, 0))
+        b_k = tl.load(p_k, boundary_check=(0, 1))
+        b_kb = b_k * b_beta[:, None]
+        b_A += tl.dot(b_kb.to(b_k.dtype), tl.trans(b_k))
+
+    if USE_G:
+        p_g = tl.make_block_ptr(g_cumsum + bos * H + i_h, (T, ), (H, ),
+                                (i_t * BT, ), (BT, ), (0, ))
+        b_g = tl.load(p_g, boundary_check=(0, ))
+        b_g_diff = b_g[:, None] - b_g[None, :]
+        b_A = b_A * safe_exp(b_g_diff)
+
+    b_A = tl.where(o_t[:, None] > o_t[None, :], b_A, 0)
+    p_A = tl.make_block_ptr(A + (bos * H + i_h) * BT, (T, BT), (BT * H, 1),
+                            (i_t * BT, 0), (BT, BT), (1, 0))
+    tl.store(p_A, b_A.to(p_A.dtype.element_ty), boundary_check=(0, 1))
+
+
+def chunk_scaled_dot_kkt_fwd(
+        k: torch.Tensor,
+        beta: torch.Tensor,
+        g_cumsum: Optional[torch.Tensor] = None,
+        cu_seqlens: Optional[torch.LongTensor] = None,
+        chunk_size: int = 64,
+        output_dtype: torch.dtype = torch.float32) -> torch.Tensor:
+    r"""
+    Compute beta * K * K^T.
+
+    Args:
+        k (torch.Tensor):
+            The key tensor of shape `[B, T, H, K]`.
+        beta (torch.Tensor):
+            The beta tensor of shape `[B, T, H]`.
+        g_cumsum (torch.Tensor):
+            The cumulative sum of the gate tensor of shape `[B, T, H]`.
+            Default: None
+        cu_seqlens (torch.LongTensor):
+            The cumulative sequence lengths of the input tensor.
+            Default: None
+        chunk_size (int):
+            The chunk size. Default: 64.
+        output_dtype (torch.dtype):
+            The dtype of the output tensor. Default: `torch.float32`
+
+    Returns:
+        beta * K * K^T of shape `[B, T, H, BT]` where `BT` is the chunk size.
+    """
+
+    B, T, Hg, K = k.shape
+
+    H = beta.shape[-1]
+    BT = chunk_size
+    chunk_indices = prepare_chunk_indices(
+        cu_seqlens, BT) if cu_seqlens is not None else None
+    NT = triton.cdiv(T, BT) if cu_seqlens is None else len(chunk_indices)
+    A = torch.empty(B, T, H, BT, device=k.device, dtype=output_dtype)
+    chunk_scaled_dot_kkt_fwd_kernel[(NT, B * H)](
+        k=k,
+        beta=beta,
+        g_cumsum=g_cumsum,
+        A=A,
+        cu_seqlens=cu_seqlens,
+        chunk_indices=chunk_indices,
+        T=T,
+        H=H,
+        Hg=Hg,
+        K=K,
+        BT=BT,
+    )
+    return A

vllm/model_executor/layers/fla/ops/cumsum.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+# ruff: noqa: E501
+import warnings
+from typing import Optional
+
+import torch
+
+from vllm.triton_utils import tl, triton
+
+from .index import prepare_chunk_indices
+from .utils import check_shared_mem, input_guard
+
+BS_LIST = [32, 64] if check_shared_mem() else [16, 32]
+
+
+@triton.heuristics({'IS_VARLEN': lambda args: args['cu_seqlens'] is not None})
+@triton.autotune(configs=[
+    triton.Config({}, num_warps=num_warps) for num_warps in [1, 2, 4, 8]
+],
+                 key=['B', 'H', 'BT', 'IS_VARLEN', 'REVERSE'])
+@triton.jit(do_not_specialize=['T'])
+def chunk_local_cumsum_scalar_kernel(
+    s,
+    o,
+    cu_seqlens,
+    chunk_indices,
+    T,
+    B: tl.constexpr,
+    H: tl.constexpr,
+    BT: tl.constexpr,
+    REVERSE: tl.constexpr,
+    IS_VARLEN: tl.constexpr,
+    HEAD_FIRST: tl.constexpr,
+):
+    i_t, i_bh = tl.program_id(0), tl.program_id(1)
+    i_b, i_h = i_bh // H, i_bh % H
+    if IS_VARLEN:
+        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(
+            tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+    else:
+        bos, eos = i_b * T, i_b * T + T
+
+    if HEAD_FIRST:
+        p_s = tl.make_block_ptr(s + bos * H + i_h * T, (T, ), (1, ),
+                                (i_t * BT, ), (BT, ), (0, ))
+        p_o = tl.make_block_ptr(o + bos * H + i_h * T, (T, ), (1, ),
+                                (i_t * BT, ), (BT, ), (0, ))
+    else:
+        p_s = tl.make_block_ptr(s + bos * H + i_h, (T, ), (H, ), (i_t * BT, ),
+                                (BT, ), (0, ))
+        p_o = tl.make_block_ptr(o + bos * H + i_h, (T, ), (H, ), (i_t * BT, ),
+                                (BT, ), (0, ))
+    # [BT]
+    b_s = tl.load(p_s, boundary_check=(0, )).to(tl.float32)
+    b_o = tl.cumsum(b_s, axis=0)
+    if REVERSE:
+        b_z = tl.sum(b_s, axis=0)
+        b_o = -b_o + b_z[None] + b_s
+    tl.store(p_o, b_o.to(p_o.dtype.element_ty), boundary_check=(0, ))
+
+
+@triton.heuristics({'IS_VARLEN': lambda args: args['cu_seqlens'] is not None})
+@triton.autotune(configs=[
+    triton.Config({'BS': BS}, num_warps=num_warps) for BS in BS_LIST
+    for num_warps in [2, 4, 8]
+],
+                 key=['B', 'H', 'S', 'BT', 'IS_VARLEN', 'REVERSE'])
+@triton.jit(do_not_specialize=['T'])
+def chunk_local_cumsum_vector_kernel(
+    s,
+    o,
+    cu_seqlens,
+    chunk_indices,
+    T,
+    B: tl.constexpr,
+    H: tl.constexpr,
+    S: tl.constexpr,
+    BT: tl.constexpr,
+    BS: tl.constexpr,
+    REVERSE: tl.constexpr,
+    IS_VARLEN: tl.constexpr,
+    HEAD_FIRST: tl.constexpr,
+):
+    i_s, i_t, i_bh = tl.program_id(0), tl.program_id(1), tl.program_id(2)
+    i_b, i_h = i_bh // H, i_bh % H
+    if IS_VARLEN:
+        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(
+            tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+    else:
+        bos, eos = i_b * T, i_b * T + T
+
+    o_i = tl.arange(0, BT)
+    if REVERSE:
+        m_s = tl.where(o_i[:, None] <= o_i[None, :], 1., 0.)
+    else:
+        m_s = tl.where(o_i[:, None] >= o_i[None, :], 1., 0.)
+
+    if HEAD_FIRST:
+        p_s = tl.make_block_ptr(s + (bos * H + i_h * T) * S, (T, S), (S, 1),
+                                (i_t * BT, i_s * BS), (BT, BS), (1, 0))
+        p_o = tl.make_block_ptr(o + (bos * H + i_h * T) * S, (T, S), (S, 1),
+                                (i_t * BT, i_s * BS), (BT, BS), (1, 0))
+    else:
+        p_s = tl.make_block_ptr(s + (bos * H + i_h) * S, (T, S), (H * S, 1),
+                                (i_t * BT, i_s * BS), (BT, BS), (1, 0))
+        p_o = tl.make_block_ptr(o + (bos * H + i_h) * S, (T, S), (H * S, 1),
+                                (i_t * BT, i_s * BS), (BT, BS), (1, 0))
+    # [BT, BS]
+    b_s = tl.load(p_s, boundary_check=(0, 1)).to(tl.float32)
+    b_o = tl.dot(m_s, b_s, allow_tf32=False)
+    tl.store(p_o, b_o.to(p_o.dtype.element_ty), boundary_check=(0, 1))
+
+
+def chunk_local_cumsum_scalar(
+        g: torch.Tensor,
+        chunk_size: int,
+        reverse: bool = False,
+        cu_seqlens: Optional[torch.Tensor] = None,
+        head_first: bool = False,
+        output_dtype: Optional[torch.dtype] = torch.float) -> torch.Tensor:
+    if head_first:
+        B, H, T = g.shape
+    else:
+        B, T, H = g.shape
+    assert chunk_size == 2**(chunk_size.bit_length() -
+                             1), "chunk_size must be a power of 2"
+    BT = chunk_size
+    chunk_indices = prepare_chunk_indices(
+        cu_seqlens, BT) if cu_seqlens is not None else None
+    NT = triton.cdiv(T, BT) if cu_seqlens is None else len(chunk_indices)
+    g_org, g = g, torch.empty_like(g, dtype=output_dtype or g.dtype)
+    grid = (NT, B * H)
+    chunk_local_cumsum_scalar_kernel[grid](g_org,
+                                           g,
+                                           cu_seqlens,
+                                           chunk_indices,
+                                           T=T,
+                                           B=B,
+                                           H=H,
+                                           BT=BT,
+                                           HEAD_FIRST=head_first,
+                                           REVERSE=reverse)
+    return g
+
+
+def chunk_local_cumsum_vector(
+        g: torch.Tensor,
+        chunk_size: int,
+        reverse: bool = False,
+        cu_seqlens: Optional[torch.Tensor] = None,
+        head_first: bool = False,
+        output_dtype: Optional[torch.dtype] = torch.float) -> torch.Tensor:
+    if head_first:
+        B, H, T, S = g.shape
+    else:
+        B, T, H, S = g.shape
+    BT = chunk_size
+    chunk_indices = prepare_chunk_indices(
+        cu_seqlens, chunk_size) if cu_seqlens is not None else None
+    NT = triton.cdiv(T, BT) if cu_seqlens is None else len(chunk_indices)
+    assert chunk_size == 2**(chunk_size.bit_length() -
+                             1), "chunk_size must be a power of 2"
+
+    g_org, g = g, torch.empty_like(g, dtype=output_dtype or g.dtype)
+
+    def grid(meta):
+        return (triton.cdiv(meta['S'], meta['BS']), NT, B * H)
+
+    # keep cummulative normalizer in fp32
+    # this kernel is equivalent to
+    # g = g.view(B, H, NT, BT, -1).cumsum(-2).view(B, H, T, -1)
+    chunk_local_cumsum_vector_kernel[grid](g_org,
+                                           g,
+                                           cu_seqlens,
+                                           chunk_indices,
+                                           T=T,
+                                           B=B,
+                                           H=H,
+                                           S=S,
+                                           BT=BT,
+                                           HEAD_FIRST=head_first,
+                                           REVERSE=reverse)
+    return g
+
+
+@input_guard
+def chunk_local_cumsum(g: torch.Tensor,
+                       chunk_size: int,
+                       reverse: bool = False,
+                       cu_seqlens: Optional[torch.Tensor] = None,
+                       head_first: bool = False,
+                       output_dtype: Optional[torch.dtype] = torch.float,
+                       **kwargs) -> torch.Tensor:
+    if not head_first and g.shape[1] < g.shape[2]:
+        warnings.warn(
+            f"Input tensor shape suggests potential format mismatch: seq_len ({g.shape[1]}) < num_heads ({g.shape[2]}). "
+            "This may indicate the inputs were passed in head-first format [B, H, T, ...] "
+            "when head_first=False was specified. "
+            "Please verify your input tensor format matches the expected shape [B, T, H, ...].",
+            stacklevel=2)
+    if cu_seqlens is not None:
+        assert g.shape[
+            0] == 1, "Only batch size 1 is supported when cu_seqlens are provided"
+    if len(g.shape) == 3:
+        return chunk_local_cumsum_scalar(g, chunk_size, reverse, cu_seqlens,
+                                         head_first, output_dtype)
+    elif len(g.shape) == 4:
+        return chunk_local_cumsum_vector(g, chunk_size, reverse, cu_seqlens,
+                                         head_first, output_dtype)
+    else:
+        raise ValueError(f"Unsupported input shape {g.shape}. "
+                         f"which should be (B, T, H, D) if `head_first=False` "
+                         f"or (B, H, T, D) otherwise")

vllm/model_executor/layers/fla/ops/fused_recurrent.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+# ruff: noqa: E501
+from typing import Optional
+
+import torch
+
+from vllm.triton_utils import tl, triton
+
+from .op import exp
+
+
+@triton.heuristics({
+    'USE_INITIAL_STATE':
+    lambda args: args['h0'] is not None,
+    'IS_VARLEN':
+    lambda args: args['cu_seqlens'] is not None,
+    "IS_CONTINUOUS_BATCHING":
+    lambda args: args['ssm_state_indices'] is not None,
+    "IS_SPEC_DECODING":
+    lambda args: args['num_accepted_tokens'] is not None,
+})
+@triton.jit(do_not_specialize=['N', 'T'])
+def fused_recurrent_gated_delta_rule_fwd_kernel(
+    q,
+    k,
+    v,
+    g,
+    beta,
+    o,
+    h0,
+    ht,
+    cu_seqlens,
+    ssm_state_indices,
+    num_accepted_tokens,
+    scale,
+    N: tl.constexpr,  # num of sequences
+    T: tl.constexpr,  # num of tokens
+    B: tl.constexpr,
+    H: tl.constexpr,
+    HV: tl.constexpr,
+    K: tl.constexpr,
+    V: tl.constexpr,
+    BK: tl.constexpr,
+    BV: tl.constexpr,
+    stride_init_state_token: tl.constexpr,
+    stride_final_state_token: tl.constexpr,
+    stride_indices_seq: tl.constexpr,
+    stride_indices_tok: tl.constexpr,
+    USE_INITIAL_STATE: tl.constexpr,  # whether to use initial state
+    INPLACE_FINAL_STATE: tl.constexpr,  # whether to store final state inplace
+    IS_BETA_HEADWISE: tl.
+    constexpr,  # whether beta is headwise vector or scalar,
+    USE_QK_L2NORM_IN_KERNEL: tl.constexpr,
+    IS_VARLEN: tl.constexpr,
+    IS_CONTINUOUS_BATCHING: tl.constexpr,
+    IS_SPEC_DECODING: tl.constexpr,
+):
+    i_k, i_v, i_nh = tl.program_id(0), tl.program_id(1), tl.program_id(2)
+    i_n, i_hv = i_nh // HV, i_nh % HV
+    i_h = i_hv // (HV // H)
+    if IS_VARLEN:
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int64), tl.load(cu_seqlens + i_n + 1).to(tl.int64)
+        all = T
+        T = eos - bos
+    else:
+        bos, eos = i_n * T, i_n * T + T
+        all = B * T
+
+    if T == 0:
+        # no tokens to process for this sequence
+        return
+
+    o_k = i_k * BK + tl.arange(0, BK)
+    o_v = i_v * BV + tl.arange(0, BV)
+
+    p_q = q + (bos * H + i_h) * K + o_k
+    p_k = k + (bos * H + i_h) * K + o_k
+    p_v = v + (bos * HV + i_hv) * V + o_v
+    if IS_BETA_HEADWISE:
+        p_beta = beta + (bos * HV + i_hv) * V + o_v
+    else:
+        p_beta = beta + bos * HV + i_hv
+    p_g = g + bos * HV + i_hv
+    p_o = o + ((i_k * all + bos) * HV + i_hv) * V + o_v
+
+    mask_k = o_k < K
+    mask_v = o_v < V
+    mask_h = mask_k[:, None] & mask_v[None, :]
+
+    b_h = tl.zeros([BK, BV], dtype=tl.float32)
+    if USE_INITIAL_STATE:
+        if IS_CONTINUOUS_BATCHING:
+            if IS_SPEC_DECODING:
+                i_t = tl.load(num_accepted_tokens + i_n).to(tl.int64) - 1
+            else:
+                i_t = 0
+            p_h0 = h0 + tl.load(ssm_state_indices + i_n * stride_indices_seq +
+                                i_t).to(tl.int64) * stride_init_state_token
+        else:
+            p_h0 = h0 + bos * HV * K * V
+        p_h0 = p_h0 + i_hv * K * V + o_k[:, None] * V + o_v[None, :]
+        b_h += tl.load(p_h0, mask=mask_h, other=0).to(tl.float32)
+
+    for i_t in range(0, T):
+        b_q = tl.load(p_q, mask=mask_k, other=0).to(tl.float32)
+        b_k = tl.load(p_k, mask=mask_k, other=0).to(tl.float32)
+        b_v = tl.load(p_v, mask=mask_v, other=0).to(tl.float32)
+        b_g = tl.load(p_g).to(tl.float32)
+
+        if USE_QK_L2NORM_IN_KERNEL:
+            b_q = b_q / (tl.sqrt(tl.sum(b_q * b_q)) + 1e-6)
+            b_k = b_k / (tl.sqrt(tl.sum(b_k * b_k)) + 1e-6)
+        b_q = b_q * scale
+        # [BK, BV]
+        b_h *= exp(b_g)
+        # [BV]
+        b_v -= tl.sum(b_h * b_k[:, None], 0)
+        if IS_BETA_HEADWISE:
+            b_beta = tl.load(p_beta, mask=mask_v, other=0).to(tl.float32)
+        else:
+            b_beta = tl.load(p_beta).to(tl.float32)
+        b_v *= b_beta
+        # [BK, BV]
+        b_h += b_k[:, None] * b_v[None, :]
+        # [BV]
+        b_o = tl.sum(b_h * b_q[:, None], 0)
+        tl.store(p_o, b_o.to(p_o.dtype.element_ty), mask=mask_v)
+
+        # keep the states for multi-query tokens
+        if INPLACE_FINAL_STATE:
+            p_ht = ht + tl.load(ssm_state_indices + i_n * stride_indices_seq +
+                                i_t).to(tl.int64) * stride_final_state_token
+        else:
+            p_ht = ht + (bos + i_t) * stride_final_state_token
+        p_ht = p_ht + i_hv * K * V + o_k[:, None] * V + o_v[None, :]
+        tl.store(p_ht, b_h.to(p_ht.dtype.element_ty), mask=mask_h)
+
+        p_q += H * K
+        p_k += H * K
+        p_o += HV * V
+        p_v += HV * V
+        p_g += HV
+        p_beta += HV * (V if IS_BETA_HEADWISE else 1)
+
+
+def fused_recurrent_gated_delta_rule_fwd(
+    q: torch.Tensor,
+    k: torch.Tensor,
+    v: torch.Tensor,
+    g: torch.Tensor,
+    beta: torch.Tensor,
+    scale: float,
+    initial_state: torch.Tensor,
+    inplace_final_state: bool = True,
+    cu_seqlens: Optional[torch.LongTensor] = None,
+    ssm_state_indices: Optional[torch.Tensor] = None,
+    num_accepted_tokens: Optional[torch.Tensor] = None,
+    use_qk_l2norm_in_kernel: bool = False,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    B, T, H, K, V = *k.shape, v.shape[-1]
+    HV = v.shape[2]
+    N = B if cu_seqlens is None else len(cu_seqlens) - 1
+    BK, BV = triton.next_power_of_2(K), min(triton.next_power_of_2(V), 8)
+    NK, NV = triton.cdiv(K, BK), triton.cdiv(V, BV)
+    assert NK == 1, "NK > 1 is not supported yet"
+    num_stages = 3
+    num_warps = 1
+
+    o = q.new_empty(NK, *v.shape)
+    if inplace_final_state:
+        final_state = initial_state
+    else:
+        final_state = q.new_empty(T, HV, K, V, dtype=initial_state.dtype)
+
+    stride_init_state_token = initial_state.stride(0)
+    stride_final_state_token = final_state.stride(0)
+
+    if ssm_state_indices is None:
+        stride_indices_seq, stride_indices_tok = 1, 1
+    elif ssm_state_indices.ndim == 1:
+        stride_indices_seq, stride_indices_tok = ssm_state_indices.stride(0), 1
+    else:
+        stride_indices_seq, stride_indices_tok = ssm_state_indices.stride()
+
+    grid = (NK, NV, N * HV)
+    fused_recurrent_gated_delta_rule_fwd_kernel[grid](
+        q=q,
+        k=k,
+        v=v,
+        g=g,
+        beta=beta,
+        o=o,
+        h0=initial_state,
+        ht=final_state,
+        cu_seqlens=cu_seqlens,
+        ssm_state_indices=ssm_state_indices,
+        num_accepted_tokens=num_accepted_tokens,
+        scale=scale,
+        N=N,
+        T=T,
+        B=B,
+        H=H,
+        HV=HV,
+        K=K,
+        V=V,
+        BK=BK,
+        BV=BV,
+        stride_init_state_token=stride_init_state_token,
+        stride_final_state_token=stride_final_state_token,
+        stride_indices_seq=stride_indices_seq,
+        stride_indices_tok=stride_indices_tok,
+        IS_BETA_HEADWISE=beta.ndim == v.ndim,
+        USE_QK_L2NORM_IN_KERNEL=use_qk_l2norm_in_kernel,
+        INPLACE_FINAL_STATE=inplace_final_state,
+        num_warps=num_warps,
+        num_stages=num_stages,
+    )
+    o = o.squeeze(0)
+    return o, final_state
+
+
+class FusedRecurrentFunction(torch.autograd.Function):
+
+    @staticmethod
+    def forward(ctx,
+                q: torch.Tensor,
+                k: torch.Tensor,
+                v: torch.Tensor,
+                g: torch.Tensor,
+                beta: torch.Tensor,
+                scale: float,
+                initial_state: torch.Tensor,
+                inplace_final_state: bool = True,
+                cu_seqlens: Optional[torch.LongTensor] = None,
+                ssm_state_indices: Optional[torch.Tensor] = None,
+                num_accepted_tokens: Optional[torch.Tensor] = None,
+                use_qk_l2norm_in_kernel: bool = False):
+        o, final_state = fused_recurrent_gated_delta_rule_fwd(
+            q=q.contiguous(),
+            k=k.contiguous(),
+            v=v.contiguous(),
+            g=g.contiguous(),
+            beta=beta.contiguous(),
+            scale=scale,
+            initial_state=initial_state,
+            inplace_final_state=inplace_final_state,
+            cu_seqlens=cu_seqlens,
+            ssm_state_indices=ssm_state_indices,
+            num_accepted_tokens=num_accepted_tokens,
+            use_qk_l2norm_in_kernel=use_qk_l2norm_in_kernel,
+        )
+
+        return o, final_state
+
+
+def fused_recurrent_gated_delta_rule(
+    q: torch.Tensor,
+    k: torch.Tensor,
+    v: torch.Tensor,
+    g: torch.Tensor,
+    beta: torch.Tensor = None,
+    scale: float = None,
+    initial_state: torch.Tensor = None,
+    inplace_final_state: bool = True,
+    cu_seqlens: Optional[torch.LongTensor] = None,
+    ssm_state_indices: Optional[torch.Tensor] = None,
+    num_accepted_tokens: Optional[torch.Tensor] = None,
+    use_qk_l2norm_in_kernel: bool = False,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    r"""
+    Args:
+        q (torch.Tensor):
+            queries of shape `[B, T, H, K]`.
+        k (torch.Tensor):
+            keys of shape `[B, T, H, K]`.
+        v (torch.Tensor):
+            values of shape `[B, T, HV, V]`.
+            GVA is applied if `HV > H`.
+        g (torch.Tensor):
+            g (decays) of shape `[B, T, HV]`.
+        beta (torch.Tensor):
+            betas of shape `[B, T, HV]`.
+        scale (Optional[int]):
+            Scale factor for the RetNet attention scores.
+            If not provided, it will default to `1 / sqrt(K)`. Default: `None`.
+        initial_state (Optional[torch.Tensor]):
+            Initial state of shape `[N, HV, K, V]` for `N` input sequences.
+            For equal-length input sequences, `N` equals the batch size `B`.
+            Default: `None`.
+        inplace_final_state: bool:
+            Whether to store the final state in-place to save memory.
+            Default: `True`.
+        cu_seqlens (torch.LongTensor):
+            Cumulative sequence lengths of shape `[N+1]` used for variable-length training,
+            consistent with the FlashAttention API.
+        ssm_state_indices (Optional[torch.Tensor]):
+            Indices to map the input sequences to the initial/final states.
+        num_accepted_tokens (Optional[torch.Tensor]):
+            Number of accepted tokens for each sequence during decoding.
+
+    Returns:
+        o (torch.Tensor):
+            Outputs of shape `[B, T, HV, V]`.
+        final_state (torch.Tensor):
+            Final state of shape `[N, HV, K, V]`.
+
+    Examples::
+        >>> import torch
+        >>> import torch.nn.functional as F
+        >>> from einops import rearrange
+        >>> from fla.ops.gated_delta_rule import fused_recurrent_gated_delta_rule
+        # inputs with equal lengths
+        >>> B, T, H, HV, K, V = 4, 2048, 4, 8, 512, 512
+        >>> q = torch.randn(B, T, H, K, device='cuda')
+        >>> k = F.normalize(torch.randn(B, T, H, K, device='cuda'), p=2, dim=-1)
+        >>> v = torch.randn(B, T, HV, V, device='cuda')
+        >>> g = F.logsigmoid(torch.rand(B, T, HV, device='cuda'))
+        >>> beta = torch.rand(B, T, HV, device='cuda').sigmoid()
+        >>> h0 = torch.randn(B, HV, K, V, device='cuda')
+        >>> o, ht = fused_gated_recurrent_delta_rule(
+            q, k, v, g, beta,
+            initial_state=h0,
+        )
+        # for variable-length inputs, the batch size `B` is expected to be 1 and `cu_seqlens` is required
+        >>> q, k, v, g, beta = map(lambda x: rearrange(x, 'b t ... -> 1 (b t) ...'), (q, k, v, g, beta))
+        # for a batch with 4 sequences, `cu_seqlens` with 5 start/end positions are expected
+        >>> cu_seqlens = q.new_tensor([0, 2048, 4096, 6144, 8192], dtype=torch.long)
+        >>> o_var, ht_var = fused_gated_recurrent_delta_rule(
+            q, k, v, g, beta,
+            initial_state=h0,
+            cu_seqlens=cu_seqlens
+        )
+    """
+    if cu_seqlens is not None and q.shape[0] != 1:
+        raise ValueError(
+            f"The batch size is expected to be 1 rather than {q.shape[0]} when using `cu_seqlens`."
+            f"Please flatten variable-length inputs before processing.")
+    if scale is None:
+        scale = k.shape[-1]**-0.5
+    else:
+        assert scale > 0, "scale must be positive"
+    if beta is None:
+        beta = torch.ones_like(q[..., 0])
+    o, final_state = FusedRecurrentFunction.apply(
+        q,
+        k,
+        v,
+        g,
+        beta,
+        scale,
+        initial_state,
+        inplace_final_state,
+        cu_seqlens,
+        ssm_state_indices,
+        num_accepted_tokens,
+        use_qk_l2norm_in_kernel,
+    )
+    return o, final_state

vllm/model_executor/layers/fla/ops/index.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+# ruff: noqa: E501
+import torch
+
+from vllm.triton_utils import triton
+
+from .utils import tensor_cache
+
+
+@tensor_cache
+def prepare_lens(cu_seqlens: torch.LongTensor) -> torch.LongTensor:
+    return cu_seqlens[1:] - cu_seqlens[:-1]
+
+
+@tensor_cache
+def prepare_chunk_indices(cu_seqlens: torch.LongTensor,
+                          chunk_size: int) -> torch.LongTensor:
+    indices = torch.cat([
+        torch.arange(n)
+        for n in triton.cdiv(prepare_lens(cu_seqlens), chunk_size).tolist()
+    ])
+    return torch.stack([indices.eq(0).cumsum(0) - 1, indices],
+                       1).to(cu_seqlens)
+
+
+@tensor_cache
+def prepare_chunk_offsets(cu_seqlens: torch.LongTensor,
+                          chunk_size: int) -> torch.LongTensor:
+    return torch.cat([
+        cu_seqlens.new_tensor([0]),
+        triton.cdiv(prepare_lens(cu_seqlens), chunk_size)
+    ]).cumsum(-1)

vllm/model_executor/layers/fla/ops/l2norm.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+
+import os
+from typing import Optional
+
+import torch
+
+from vllm.triton_utils import tl, triton
+
+BT_LIST = [8, 16, 32, 64, 128]
+
+USE_DEFAULT_FLA_NORM = int(os.getenv("USE_DEFAULT_FLA_NORM", "0"))
+
+
+@triton.autotune(configs=[
+    triton.Config({}, num_warps=num_warps)
+    for num_warps in [1, 2, 4, 8, 16, 32]
+],
+                 key=['D'])
+@triton.jit
+def l2norm_fwd_kernel1(
+    x,
+    y,
+    D,
+    BD: tl.constexpr,
+    eps,
+):
+    i_t = tl.program_id(0)
+    x += i_t * D
+    y += i_t * D
+    # Compute mean and variance
+    cols = tl.arange(0, BD)
+    mask = cols < D
+    b_x = tl.load(x + cols, mask=mask, other=0.0).to(tl.float32)
+    b_var = tl.sum(b_x * b_x, axis=0)
+    b_rstd = 1 / tl.sqrt(b_var + eps)
+    # tl.store(Rstd + i_t, rstd)
+    # Normalize and apply linear transformation
+    b_y = b_x * b_rstd
+    tl.store(y + cols, b_y, mask=mask)
+
+
+@triton.autotune(configs=[
+    triton.Config({'BT': BT}, num_warps=num_warps)
+    for num_warps in [1, 2, 4, 8, 16] for BT in BT_LIST
+],
+                 key=['D'])
+@triton.jit(do_not_specialize=["NB"])
+def l2norm_fwd_kernel(
+    x,
+    y,
+    eps,
+    NB,
+    T,
+    D: tl.constexpr,
+    BT: tl.constexpr,
+    BD: tl.constexpr,
+):
+    i_t = tl.program_id(0)
+    p_x = tl.make_block_ptr(x, (T, D), (D, 1), (i_t * BT, 0), (BT, BD), (1, 0))
+    b_x = tl.load(p_x, boundary_check=(0, 1)).to(tl.float32)
+    b_var = tl.sum(b_x * b_x, axis=1)
+    b_y = b_x / tl.sqrt(b_var + eps)[:, None]
+    p_y = tl.make_block_ptr(y, (T, D), (D, 1), (i_t * BT, 0), (BT, BD), (1, 0))
+    tl.store(p_y, b_y.to(p_y.dtype.element_ty), boundary_check=(0, 1))
+
+
+@triton.jit
+def l2norm_fwd_kernel2(X, Y, eps, M, N: tl.constexpr, MBLOCK: tl.constexpr):
+    xoffset = tl.program_id(0) * MBLOCK
+    row_idx = xoffset + tl.arange(0, MBLOCK)[:, None]
+    xmask = row_idx < M
+    rindex = tl.arange(0, N)[None, :]
+    xs = tl.load(X + (rindex + N * row_idx), None).to(tl.float32)
+    square = tl.broadcast_to(xs * xs, [MBLOCK, N])
+    square_sum = tl.sum(tl.where(xmask, square, 0), 1)[:, None]
+    rsqrt = tl.rsqrt(square_sum + eps)
+    tl.store(Y + (rindex + N * row_idx), xs * rsqrt, xmask)
+
+
+def l2norm_fwd(x: torch.Tensor,
+               eps: float = 1e-6,
+               output_dtype: Optional[torch.dtype] = None):
+    x_shape_og = x.shape
+    x = x.view(-1, x.shape[-1])
+    # allocate output
+    if output_dtype is None:
+        y = torch.empty_like(x)
+    else:
+        y = torch.empty_like(x, dtype=output_dtype)
+    assert y.stride(-1) == 1
+    T, D = x.shape[0], x.shape[-1]
+    # rstd = torch.empty((T,), dtype=torch.float32, device=x.device)
+    # Less than 64KB per feature: enqueue fused kernel
+    MAX_FUSED_SIZE = 65536 // x.element_size()
+    BD = min(MAX_FUSED_SIZE, triton.next_power_of_2(D))
+    if D > BD:
+        raise RuntimeError("This layer doesn't support feature dim >= 64KB.")
+
+    if not USE_DEFAULT_FLA_NORM:
+        MBLOCK = 32
+        # M, N = x.shape
+        l2norm_fwd_kernel2[(triton.cdiv(T, MBLOCK), )](
+            x,
+            y,
+            eps,
+            T,
+            D,
+            MBLOCK,
+        )
+    else:
+        if D <= 512:
+            NB = triton.cdiv(T, 2048)
+
+            def grid(meta):
+                return (triton.cdiv(T, meta['BT']), )
+
+            l2norm_fwd_kernel[grid](
+                x,
+                y,
+                eps,
+                NB=NB,
+                T=T,
+                D=D,
+                BD=BD,
+            )
+        else:
+            l2norm_fwd_kernel1[(T, )](
+                x,
+                y,
+                eps=eps,
+                D=D,
+                BD=BD,
+            )
+
+    return y.view(x_shape_og)

vllm/model_executor/layers/fla/ops/layernorm_guard.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Tri Dao
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2024, Tri Dao.
+
+# ruff: noqa: E501
+# Based on the Triton LayerNorm tutorial: https://triton-lang.org/main/getting-started/tutorials/05-layer-norm.html
+# For the backward pass, we keep weight_grad and bias_grad in registers and accumulate.
+# This backward pass is faster for dimensions up to 8k, but after that it's much slower due to register spilling.
+# The models we train have hidden dim up to 8k anyway (e.g. Llama 70B), so this is fine.
+
+from typing import Optional
+
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+from einops import rearrange
+
+from vllm.triton_utils import tl, triton
+
+from .utils import input_guard
+
+
+def rms_norm_ref(x,
+                 weight,
+                 bias,
+                 z=None,
+                 eps=1e-6,
+                 group_size=None,
+                 norm_before_gate=True,
+                 upcast=True):
+    dtype = x.dtype
+    weight = weight.float()
+    bias = bias.float() if bias is not None else None
+    if upcast:
+        x = x.float()
+        z = z.float() if z is not None else z
+    if z is not None and not norm_before_gate:
+        x = x * F.silu(z)
+    if group_size is None:
+        rstd = 1 / torch.sqrt((x.square()).mean(dim=-1, keepdim=True) + eps)
+        out = (x * rstd * weight) + bias if bias is not None else (x * rstd *
+                                                                   weight)
+    else:
+        x_group = rearrange(x, "... (g d) -> ... g d", d=group_size)
+        rstd = 1 / torch.sqrt((x_group.square()).mean(dim=-1, keepdim=True) +
+                              eps)
+        out = rearrange(x_group * rstd, "... g d -> ... (g d)") * weight
+        if bias is not None:
+            out = out + bias
+    if z is not None and norm_before_gate:
+        out *= F.silu(z)
+    return out.to(dtype)
+
+
+@triton.heuristics({
+    "HAS_BIAS": lambda args: args["B"] is not None,
+    "HAS_Z": lambda args: args["Z"] is not None,
+})
+@triton.jit
+def layer_norm_fwd_kernel(
+    X,  # pointer to the input
+    Y,  # pointer to the output
+    W,  # pointer to the weights
+    B,  # pointer to the biases
+    Z,  # pointer to the other branch
+    Mean,  # pointer to the mean
+    Rstd,  # pointer to the 1/std
+    stride_x_row,  # how much to increase the pointer when moving by 1 row
+    stride_y_row,
+    stride_z_row,
+    M,  # number of rows in X
+    N,  # number of columns in X
+    eps,  # epsilon to avoid division by zero
+    BLOCK_N: tl.constexpr,
+    HAS_BIAS: tl.constexpr,
+    HAS_Z: tl.constexpr,
+    NORM_BEFORE_GATE: tl.constexpr,
+    IS_RMS_NORM: tl.constexpr,
+):
+    # Map the program id to the row of X and Y it should compute.
+    row = tl.program_id(0)
+    group = tl.program_id(1)
+    X += row * stride_x_row + group * N
+    Y += row * stride_y_row + group * N
+    if HAS_Z:
+        Z += row * stride_z_row + group * N
+    if not IS_RMS_NORM:
+        Mean += group * M
+    Rstd += group * M
+    W += group * N
+    if HAS_BIAS:
+        B += group * N
+    # Compute mean and variance
+    cols = tl.arange(0, BLOCK_N)
+    x = tl.load(X + cols, mask=cols < N, other=0.).to(tl.float32)
+    if HAS_Z and not NORM_BEFORE_GATE:
+        z = tl.load(Z + cols, mask=cols < N).to(tl.float32)
+        x *= z * tl.sigmoid(z)
+    if not IS_RMS_NORM:
+        mean = tl.sum(x, axis=0) / N
+        tl.store(Mean + row, mean)
+        xbar = tl.where(cols < N, x - mean, 0.)
+        var = tl.sum(xbar * xbar, axis=0) / N
+    else:
+        xbar = tl.where(cols < N, x, 0.)
+        var = tl.sum(xbar * xbar, axis=0) / N
+    rstd = 1 / tl.sqrt(var + eps)
+    tl.store(Rstd + row, rstd)
+    # Normalize and apply linear transformation
+    mask = cols < N
+    w = tl.load(W + cols, mask=mask).to(tl.float32)
+    if HAS_BIAS:
+        b = tl.load(B + cols, mask=mask).to(tl.float32)
+    x_hat = (x - mean) * rstd if not IS_RMS_NORM else x * rstd
+    y = x_hat * w + b if HAS_BIAS else x_hat * w
+    if HAS_Z and NORM_BEFORE_GATE:
+        z = tl.load(Z + cols, mask=mask).to(tl.float32)
+        y *= z * tl.sigmoid(z)
+    # Write output
+    tl.store(Y + cols, y, mask=mask)
+
+
+def layer_norm_fwd(
+    x: torch.Tensor,
+    weight: torch.Tensor,
+    bias: torch.Tensor,
+    eps: float,
+    z: torch.Tensor = None,
+    out: torch.Tensor = None,
+    group_size: int = None,
+    norm_before_gate: bool = True,
+    is_rms_norm: bool = False,
+):
+    M, N = x.shape
+    if group_size is None:
+        group_size = N
+    assert N % group_size == 0
+    ngroups = N // group_size
+    assert x.stride(-1) == 1
+    if z is not None:
+        assert z.stride(-1) == 1
+        assert z.shape == (M, N)
+    assert weight.shape == (N, )
+    assert weight.stride(-1) == 1
+    if bias is not None:
+        assert bias.stride(-1) == 1
+        assert bias.shape == (N, )
+    # allocate output
+    if out is not None:
+        assert out.shape == x.shape
+    else:
+        out = torch.empty_like(x)
+    assert out.stride(-1) == 1
+    mean = torch.empty((ngroups * M, ), dtype=torch.float32,
+                       device=x.device) if not is_rms_norm else None
+    rstd = torch.empty((ngroups * M, ), dtype=torch.float32, device=x.device)
+    # Less than 64KB per feature: enqueue fused kernel
+    MAX_FUSED_SIZE = 65536 // x.element_size()
+    BLOCK_N = min(MAX_FUSED_SIZE, triton.next_power_of_2(group_size))
+    if group_size > BLOCK_N:
+        raise RuntimeError(
+            "This layer norm doesn't support feature dim >= 64KB.")
+    # heuristics for number of warps
+    num_warps = min(max(BLOCK_N // 256, 1), 8)
+    grid = (M, ngroups)
+    layer_norm_fwd_kernel[grid](x,
+                                out,
+                                weight,
+                                bias,
+                                z,
+                                mean,
+                                rstd,
+                                x.stride(0),
+                                out.stride(0),
+                                z.stride(0) if z is not None else 0,
+                                M,
+                                group_size,
+                                eps,
+                                BLOCK_N=BLOCK_N,
+                                NORM_BEFORE_GATE=norm_before_gate,
+                                IS_RMS_NORM=is_rms_norm,
+                                num_warps=num_warps)
+    return out, mean, rstd
+
+
+class LayerNormFn(torch.autograd.Function):
+
+    @input_guard
+    @staticmethod
+    def forward(ctx,
+                x,
+                weight,
+                bias,
+                z=None,
+                eps=1e-6,
+                group_size=None,
+                norm_before_gate=True,
+                is_rms_norm=False):
+        """If z is not None, we do norm(x) * silu(z) if norm_before_gate, else norm(x * silu(z))
+        """
+
+        x_shape_og = x.shape
+        # reshape input data into 2D tensor
+        x = x.reshape(-1, x.shape[-1])
+        if x.stride(-1) != 1:
+            x = x.contiguous()
+        if z is not None:
+            assert z.shape == x_shape_og
+            z = z.reshape(-1, z.shape[-1])
+            if z.stride(-1) != 1:
+                z = z.contiguous()
+        weight = weight.contiguous()
+        if bias is not None:
+            bias = bias.contiguous()
+        y, mean, rstd = layer_norm_fwd(
+            x,
+            weight,
+            bias,
+            eps,
+            z=z,
+            group_size=group_size,
+            norm_before_gate=norm_before_gate,
+            is_rms_norm=is_rms_norm,
+        )
+        ctx.save_for_backward(x, weight, bias, mean, rstd, z)
+        ctx.x_shape_og = x_shape_og
+        ctx.eps = eps
+        ctx.group_size = group_size
+        ctx.norm_before_gate = norm_before_gate
+        ctx.is_rms_norm = is_rms_norm
+        return y.reshape(x_shape_og)
+
+
+def layernorm_fn(x,
+                 weight,
+                 bias,
+                 z=None,
+                 eps=1e-6,
+                 group_size=None,
+                 norm_before_gate=True,
+                 is_rms_norm=False):
+    return LayerNormFn.apply(x, weight, bias, z, eps, group_size,
+                             norm_before_gate, is_rms_norm)
+
+
+def rmsnorm_fn(x,
+               weight,
+               bias,
+               z=None,
+               eps=1e-6,
+               group_size=None,
+               norm_before_gate=True):
+    return LayerNormFn.apply(x, weight, bias, z, eps, group_size,
+                             norm_before_gate, True)
+
+
+class LayerNormGated(nn.Module):
+
+    def __init__(
+        self,
+        hidden_size,
+        eps: float = 1e-5,
+        group_size: Optional[int] = None,
+        norm_before_gate: bool = True,
+        device: Optional[torch.device] = None,
+        dtype: Optional[torch.dtype] = None,
+    ):
+        """If group_size is not None, we do GroupNorm with each group having group_size elements.
+        group_size=None is equivalent to group_size=hidden_size (i.e. there's only 1 group).
+        """
+
+        factory_kwargs = {"device": device, "dtype": dtype}
+        super().__init__()
+        self.eps = eps
+        self.weight = nn.Parameter(torch.empty(hidden_size, **factory_kwargs))
+        self.bias = nn.Parameter(torch.empty(hidden_size, **factory_kwargs))
+        self.group_size = group_size
+        self.norm_before_gate = norm_before_gate
+        self.reset_parameters()
+
+    def reset_parameters(self):
+        torch.nn.init.ones_(self.weight)
+        torch.nn.init.zeros_(self.bias)
+
+    def forward(self, x, z=None):
+        """If z is not None, we do norm(x) * silu(z) if norm_before_gate, else norm(x * silu(z))
+        """
+        return layernorm_fn(x,
+                            self.weight,
+                            self.bias,
+                            z=z,
+                            group_size=self.group_size,
+                            eps=self.eps,
+                            norm_before_gate=self.norm_before_gate)
+
+
+class RMSNormGated(nn.Module):
+
+    def __init__(
+        self,
+        hidden_size,
+        eps: float = 1e-5,
+        group_size: Optional[int] = None,
+        norm_before_gate: bool = False,
+        device: Optional[torch.device] = None,
+        dtype: Optional[torch.dtype] = None,
+    ):
+        """If group_size is not None, we do GroupNorm with each group having group_size elements.
+        group_size=None is equivalent to group_size=hidden_size (i.e. there's only 1 group).
+        """
+        factory_kwargs = {"device": device, "dtype": dtype}
+        super().__init__()
+        self.eps = eps
+        self.weight = nn.Parameter(torch.empty(hidden_size, **factory_kwargs))
+        self.register_parameter("bias", None)
+        self.group_size = group_size
+        self.norm_before_gate = norm_before_gate
+        self.reset_parameters()
+
+    def reset_parameters(self):
+        torch.nn.init.ones_(self.weight)
+
+    def forward(self, x, z=None):
+        """If z is not None, we do norm(x) * silu(z) if norm_before_gate, else norm(x * silu(z))
+        """
+        return rmsnorm_fn(x,
+                          self.weight,
+                          self.bias,
+                          z=z,
+                          eps=self.eps,
+                          group_size=self.group_size,
+                          norm_before_gate=self.norm_before_gate)

vllm/model_executor/layers/fla/ops/op.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+
+import os
+
+from vllm.triton_utils import tl, tldevice, triton
+
+if os.environ.get('FLA_USE_FAST_OPS', '0') == '1':
+    div = tldevice.fast_dividef
+    exp = tldevice.fast_expf
+    log = tldevice.fast_logf
+    log2 = tldevice.fast_log2f
+else:
+
+    @triton.jit
+    def div_normal(x, y):
+        return x / y
+
+    div = div_normal
+    exp = tl.exp
+    log = tl.log
+    log2 = tl.log2
+
+
+@triton.jit
+def safe_exp(x):
+    return exp(tl.where(x <= 0, x, float('-inf')))
+
+
+if not hasattr(tl, 'gather'):
+
+    @triton.jit
+    def gather(src, index, axis, _builder=None):
+        # This is a fallback implementation when tl.gather is not supported
+        # In order to pass triton compiler, there is no actual gather operation
+        return src
+else:
+    gather = tl.gather

vllm/model_executor/layers/fla/ops/solve_tril.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+# ruff: noqa: E501
+from typing import Optional
+
+import torch
+
+from vllm.triton_utils import tl, triton
+
+from .index import prepare_chunk_indices
+from .utils import input_guard
+
+
+@triton.heuristics({'IS_VARLEN': lambda args: args['cu_seqlens'] is not None})
+@triton.autotune(
+    configs=[
+        triton.Config({}, num_warps=num_warps, num_stages=num_stages)
+        for num_warps in [1, 2, 4, 8] for num_stages in [2, 3, 4, 5]
+    ],
+    key=['BT'],
+)
+@triton.jit(do_not_specialize=['T'])
+def solve_tril_16x16_kernel(
+    A,
+    Ad,
+    cu_seqlens,
+    chunk_indices,
+    T,
+    H: tl.constexpr,
+    BT: tl.constexpr,
+    IS_VARLEN: tl.constexpr,
+):
+    i_t, i_bh = tl.program_id(0), tl.program_id(1)
+    i_b, i_h = i_bh // H, i_bh % H
+    if IS_VARLEN:
+        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(
+            tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+    else:
+        bos, eos = i_b * T, i_b * T + T
+
+    A = A + (bos * H + i_h) * BT
+    Ad = Ad + (bos * H + i_h) * 16
+
+    offset = (i_t * 16) % BT
+    p_A = tl.make_block_ptr(A, (T, BT), (H * BT, 1), (i_t * 16, offset),
+                            (16, 16), (1, 0))
+    p_Ai = tl.make_block_ptr(Ad, (T, 16), (H * 16, 1), (i_t * 16, 0), (16, 16),
+                             (1, 0))
+    b_A = tl.load(p_A, boundary_check=(0, 1)).to(tl.float32)
+    b_A = -tl.where(
+        tl.arange(0, 16)[:, None] > tl.arange(0, 16)[None, :], b_A, 0)
+
+    o_i = tl.arange(0, 16)
+    for i in range(1, min(16, T - i_t * 16)):
+        b_a = -tl.load(A + (i_t * 16 + i) * H * BT + o_i + offset)
+        b_a = b_a + tl.sum(b_a[:, None] * b_A, 0)
+        mask = o_i == i
+        b_A = tl.where(mask[:, None], b_a, b_A)
+    b_A += o_i[:, None] == o_i[None, :]
+    tl.store(p_Ai,
+             b_A.to(p_Ai.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+
+
+@triton.heuristics({'IS_VARLEN': lambda args: args['cu_seqlens'] is not None})
+@triton.autotune(
+    configs=[
+        triton.Config({}, num_warps=num_warps, num_stages=num_stages)
+        for num_warps in [1, 2, 4, 8] for num_stages in [2, 3, 4, 5]
+    ],
+    key=['H', 'BT', 'IS_VARLEN'],
+)
+@triton.jit(do_not_specialize=['T'])
+def merge_16x16_to_32x32_inverse_kernel(A, Ad, Ai, cu_seqlens, chunk_indices,
+                                        T, H: tl.constexpr, BT: tl.constexpr,
+                                        IS_VARLEN: tl.constexpr):
+    i_t, i_bh = tl.program_id(0), tl.program_id(1)
+    i_b, i_h = i_bh // H, i_bh % H
+    if IS_VARLEN:
+        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(
+            tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+    else:
+        bos, eos = i_b * T, i_b * T + T
+
+    A += (bos * H + i_h) * 32
+    Ad += (bos * H + i_h) * 16
+    Ai += (bos * H + i_h) * 32
+
+    p_A_21 = tl.make_block_ptr(A, (T, 32), (H * 32, 1), (i_t * 32 + 16, 0),
+                               (16, 16), (1, 0))
+    p_Ad_11 = tl.make_block_ptr(Ad, (T, 16), (H * 16, 1), (i_t * 32, 0),
+                                (16, 16), (1, 0))
+    p_Ad_22 = tl.make_block_ptr(Ad, (T, 16), (H * 16, 1), (i_t * 32 + 16, 0),
+                                (16, 16), (1, 0))
+    p_Ai_11 = tl.make_block_ptr(Ai, (T, 32), (H * 32, 1), (i_t * 32, 0),
+                                (16, 16), (1, 0))
+    p_Ai_22 = tl.make_block_ptr(Ai, (T, 32), (H * 32, 1), (i_t * 32 + 16, 16),
+                                (16, 16), (1, 0))
+    p_Ai_21 = tl.make_block_ptr(Ai, (T, 32), (H * 32, 1), (i_t * 32 + 16, 0),
+                                (16, 16), (1, 0))
+
+    A_21 = tl.load(p_A_21, boundary_check=(0, 1)).to(tl.float32)
+    Ai_11 = tl.load(p_Ad_11, boundary_check=(0, 1)).to(tl.float32)
+    Ai_22 = tl.load(p_Ad_22, boundary_check=(0, 1)).to(tl.float32)
+    Ai_21 = -tl.dot(tl.dot(Ai_22, A_21, input_precision='ieee'),
+                    Ai_11,
+                    input_precision='ieee')
+    tl.store(p_Ai_11,
+             Ai_11.to(p_Ai_11.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_22,
+             Ai_22.to(p_Ai_22.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_21,
+             Ai_21.to(p_Ai_21.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+
+
+@triton.heuristics({'IS_VARLEN': lambda args: args['cu_seqlens'] is not None})
+@triton.autotune(
+    configs=[
+        triton.Config({}, num_warps=num_warps, num_stages=num_stages)
+        for num_warps in [2, 4, 8] for num_stages in [2, 3, 4, 5]
+    ],
+    key=['H', 'BT', 'IS_VARLEN'],
+)
+@triton.jit(do_not_specialize=['T'])
+def merge_16x16_to_64x64_inverse_kernel(A, Ad, Ai, cu_seqlens, chunk_indices,
+                                        T, H: tl.constexpr, BT: tl.constexpr,
+                                        IS_VARLEN: tl.constexpr):
+    i_t, i_bh = tl.program_id(0), tl.program_id(1)
+    i_b, i_h = i_bh // H, i_bh % H
+    if IS_VARLEN:
+        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(
+            tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+    else:
+        bos, eos = i_b * T, i_b * T + T
+
+    A += (bos * H + i_h) * 64
+    Ad += (bos * H + i_h) * 16
+    Ai += (bos * H + i_h) * 64
+
+    p_A_21 = tl.make_block_ptr(A, (T, 64), (H * 64, 1), (i_t * 64 + 16, 0),
+                               (16, 16), (1, 0))
+    p_A_32 = tl.make_block_ptr(A, (T, 64), (H * 64, 1), (i_t * 64 + 32, 16),
+                               (16, 16), (1, 0))
+    p_A_31 = tl.make_block_ptr(A, (T, 64), (H * 64, 1), (i_t * 64 + 32, 0),
+                               (16, 16), (1, 0))
+    p_A_43 = tl.make_block_ptr(A, (T, 64), (H * 64, 1), (i_t * 64 + 48, 32),
+                               (16, 16), (1, 0))
+    p_A_42 = tl.make_block_ptr(A, (T, 64), (H * 64, 1), (i_t * 64 + 48, 16),
+                               (16, 16), (1, 0))
+    p_A_41 = tl.make_block_ptr(A, (T, 64), (H * 64, 1), (i_t * 64 + 48, 0),
+                               (16, 16), (1, 0))
+    p_Ad_11 = tl.make_block_ptr(Ad, (T, 16), (H * 16, 1), (i_t * 64, 0),
+                                (16, 16), (1, 0))
+    p_Ad_22 = tl.make_block_ptr(Ad, (T, 16), (H * 16, 1), (i_t * 64 + 16, 0),
+                                (16, 16), (1, 0))
+    p_Ad_33 = tl.make_block_ptr(Ad, (T, 16), (H * 16, 1), (i_t * 64 + 32, 0),
+                                (16, 16), (1, 0))
+    p_Ad_44 = tl.make_block_ptr(Ad, (T, 16), (H * 16, 1), (i_t * 64 + 48, 0),
+                                (16, 16), (1, 0))
+
+    A_21 = tl.load(p_A_21, boundary_check=(0, 1)).to(tl.float32)
+    A_32 = tl.load(p_A_32, boundary_check=(0, 1)).to(tl.float32)
+    A_31 = tl.load(p_A_31, boundary_check=(0, 1)).to(tl.float32)
+    A_43 = tl.load(p_A_43, boundary_check=(0, 1)).to(tl.float32)
+    A_42 = tl.load(p_A_42, boundary_check=(0, 1)).to(tl.float32)
+    A_41 = tl.load(p_A_41, boundary_check=(0, 1)).to(tl.float32)
+
+    Ai_11 = tl.load(p_Ad_11, boundary_check=(0, 1)).to(tl.float32)
+    Ai_22 = tl.load(p_Ad_22, boundary_check=(0, 1)).to(tl.float32)
+    Ai_33 = tl.load(p_Ad_33, boundary_check=(0, 1)).to(tl.float32)
+    Ai_44 = tl.load(p_Ad_44, boundary_check=(0, 1)).to(tl.float32)
+
+    Ai_21 = -tl.dot(tl.dot(Ai_22, A_21, input_precision='ieee'),
+                    Ai_11,
+                    input_precision='ieee')
+    Ai_32 = -tl.dot(tl.dot(Ai_33, A_32, input_precision='ieee'),
+                    Ai_22,
+                    input_precision='ieee')
+    Ai_43 = -tl.dot(tl.dot(Ai_44, A_43, input_precision='ieee'),
+                    Ai_33,
+                    input_precision='ieee')
+
+    Ai_31 = -tl.dot(Ai_33,
+                    tl.dot(A_31, Ai_11, input_precision='ieee') +
+                    tl.dot(A_32, Ai_21, input_precision='ieee'),
+                    input_precision='ieee')
+    Ai_42 = -tl.dot(Ai_44,
+                    tl.dot(A_42, Ai_22, input_precision='ieee') +
+                    tl.dot(A_43, Ai_32, input_precision='ieee'),
+                    input_precision='ieee')
+    Ai_41 = -tl.dot(Ai_44,
+                    tl.dot(A_41, Ai_11, input_precision='ieee') +
+                    tl.dot(A_42, Ai_21, input_precision='ieee') +
+                    tl.dot(A_43, Ai_31, input_precision='ieee'),
+                    input_precision='ieee')
+
+    p_Ai_11 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64, 0),
+                                (16, 16), (1, 0))
+    p_Ai_22 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 16, 16),
+                                (16, 16), (1, 0))
+    p_Ai_33 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 32, 32),
+                                (16, 16), (1, 0))
+    p_Ai_44 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 48, 48),
+                                (16, 16), (1, 0))
+    p_Ai_21 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 16, 0),
+                                (16, 16), (1, 0))
+    p_Ai_31 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 32, 0),
+                                (16, 16), (1, 0))
+    p_Ai_32 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 32, 16),
+                                (16, 16), (1, 0))
+    p_Ai_41 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 48, 0),
+                                (16, 16), (1, 0))
+    p_Ai_42 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 48, 16),
+                                (16, 16), (1, 0))
+    p_Ai_43 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 48, 32),
+                                (16, 16), (1, 0))
+    tl.store(p_Ai_11,
+             Ai_11.to(p_Ai_11.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_22,
+             Ai_22.to(p_Ai_22.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_33,
+             Ai_33.to(p_Ai_33.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_44,
+             Ai_44.to(p_Ai_44.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_21,
+             Ai_21.to(p_Ai_21.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_31,
+             Ai_31.to(p_Ai_31.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_32,
+             Ai_32.to(p_Ai_32.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_41,
+             Ai_41.to(p_Ai_41.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_42,
+             Ai_42.to(p_Ai_42.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_43,
+             Ai_43.to(p_Ai_43.dtype.element_ty, fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+
+    fill_zeros = tl.zeros((16, 16), dtype=tl.float32)
+    p_Ai_12 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64, 16),
+                                (16, 16), (1, 0))
+    p_Ai_13 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64, 32),
+                                (16, 16), (1, 0))
+    p_Ai_14 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64, 48),
+                                (16, 16), (1, 0))
+    p_Ai_23 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 16, 32),
+                                (16, 16), (1, 0))
+    p_Ai_24 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 16, 48),
+                                (16, 16), (1, 0))
+    p_Ai_34 = tl.make_block_ptr(Ai, (T, 64), (H * 64, 1), (i_t * 64 + 32, 48),
+                                (16, 16), (1, 0))
+    tl.store(p_Ai_12,
+             fill_zeros.to(p_Ai_12.dtype.element_ty,
+                           fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_13,
+             fill_zeros.to(p_Ai_13.dtype.element_ty,
+                           fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_14,
+             fill_zeros.to(p_Ai_14.dtype.element_ty,
+                           fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_23,
+             fill_zeros.to(p_Ai_23.dtype.element_ty,
+                           fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_24,
+             fill_zeros.to(p_Ai_24.dtype.element_ty,
+                           fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+    tl.store(p_Ai_34,
+             fill_zeros.to(p_Ai_34.dtype.element_ty,
+                           fp_downcast_rounding="rtne"),
+             boundary_check=(0, 1))
+
+
+@input_guard
+def solve_tril(A: torch.Tensor,
+               cu_seqlens: Optional[torch.Tensor] = None,
+               output_dtype: torch.dtype = torch.float) -> torch.Tensor:
+    """
+    Compute the inverse of the lower triangular matrix
+    A should be strictly lower triangular, i.e., A.triu() == 0.
+
+    Args:
+        A (torch.Tensor):
+            [B, T, H, K]
+        cu_seqlens (torch.Tensor):
+            The cumulative sequence lengths of the input tensor.
+            Default: None.
+        output_dtype (torch.dtype):
+            The dtype of the output tensor. Default: `torch.float`
+
+    Returns:
+        (I + A)^-1 with the same shape as A
+    """
+    assert A.shape[-1] in [16, 32, 64]
+
+    B, T, H, BT = A.shape
+    Ad = torch.empty(B,
+                     T,
+                     H,
+                     16,
+                     device=A.device,
+                     dtype=torch.float if BT != 16 else output_dtype)
+
+    chunk_indices = prepare_chunk_indices(
+        cu_seqlens, 16) if cu_seqlens is not None else None
+    NT = len(chunk_indices) if cu_seqlens is not None else triton.cdiv(T, 16)
+    solve_tril_16x16_kernel[NT, B * H](
+        A=A,
+        Ad=Ad,
+        cu_seqlens=cu_seqlens,
+        chunk_indices=chunk_indices,
+        T=T,
+        H=H,
+        BT=BT,
+    )
+    if BT == 16:
+        return Ad
+
+    Ai = torch.empty(B, T, H, BT, device=A.device, dtype=output_dtype)
+    merge_fn = merge_16x16_to_32x32_inverse_kernel if BT == 32 else merge_16x16_to_64x64_inverse_kernel
+    chunk_indices = prepare_chunk_indices(
+        cu_seqlens, BT) if cu_seqlens is not None else None
+    NT = len(chunk_indices) if cu_seqlens is not None else triton.cdiv(T, BT)
+    merge_fn[NT, B * H](
+        A=A,
+        Ad=Ad,
+        Ai=Ai,
+        cu_seqlens=cu_seqlens,
+        chunk_indices=chunk_indices,
+        T=T,
+        H=H,
+        BT=BT,
+    )
+    return Ai

vllm/model_executor/layers/fla/ops/utils.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+# ruff: noqa: E501
+import contextlib
+import functools
+import logging
+import os
+from enum import Enum
+from typing import Any, Callable, Literal, Optional
+
+import torch
+
+from vllm.triton_utils import triton
+
+logger = logging.getLogger(__name__)
+
+COMPILER_MODE = os.getenv("FLA_COMPILER_MODE") == "1"
+FLA_CI_ENV = os.getenv("FLA_CI_ENV") == "1"
+FLA_GDN_FIX_BT = os.getenv("FLA_GDN_FIX_BT", "0") == "1"
+
+SUPPRESS_LEVEL = int(os.getenv("GDN_RECOMPUTE_SUPPRESS_LEVEL", "0"))
+
+
+def tensor_cache(
+        fn: Callable[..., torch.Tensor]) -> Callable[..., torch.Tensor]:
+    """
+    A decorator that caches the most recent results of a function with tensor inputs.
+
+    This decorator will store the output of the decorated function for the most recent set of input tensors.
+    The cache is limited to a fixed size (default is 4). When the cache is full, the oldest entry will be removed.
+
+    Args:
+        fn (Callable[..., torch.Tensor]):
+            The function to be decorated. It should take tensor inputs and return tensor outputs.
+
+    Returns:
+        Callable[..., torch.Tensor]:
+            A wrapped version of the input function with single-entry caching.
+    """
+
+    cache_entries: tuple[Optional[tuple], Optional[dict], Any] = []
+    cache_size = 4
+
+    @functools.wraps(fn)
+    def wrapper(*args: Any, **kwargs: Any) -> Any:
+        nonlocal cache_entries, cache_size
+        for i, entry in enumerate(cache_entries):
+            last_args, last_kwargs, last_result = entry
+            if len(args) == len(last_args) and len(kwargs) == len(last_kwargs) \
+                and all(a is b for a, b in zip(args, last_args)) \
+                and all(k in last_kwargs and v is last_kwargs[k] for k, v in kwargs.items()):
+                cache_entries = cache_entries[:i] + cache_entries[i + 1:] + [
+                    (args, kwargs, last_result)
+                ]
+                return last_result
+
+        result = fn(*args, **kwargs)
+
+        if len(cache_entries) >= cache_size:
+            cache_entries = cache_entries[1:]
+        cache_entries.append((args, kwargs, result))
+        return result
+
+    return wrapper
+
+
+def input_guard(
+        fn: Callable[..., torch.Tensor]) -> Callable[..., torch.Tensor]:
+    """
+    A decorator to make sure all input tensors are contiguous and set the device based on input tensors.
+    """
+
+    @functools.wraps(fn)
+    def wrapper(*args, **kwargs):
+        contiguous_args = (i if not isinstance(i, torch.Tensor) else
+                           i.contiguous() for i in args)
+        contiguous_kwargs = {
+            k: (v if not isinstance(v, torch.Tensor) else v.contiguous())
+            for k, v in kwargs.items()
+        }
+
+        tensor = None
+        for arg in args:
+            if isinstance(arg, torch.Tensor):
+                tensor = arg
+                break
+        if tensor is None:
+            for value in kwargs.values():
+                if isinstance(value, torch.Tensor):
+                    tensor = value
+                    break
+
+        if tensor is not None:
+            ctx = torch.cuda.device(tensor.device.index)
+        else:
+            ctx = contextlib.nullcontext()
+
+        with ctx:
+            return fn(*contiguous_args, **contiguous_kwargs)
+
+    return wrapper
+
+
+@functools.cache
+def get_available_device() -> str:
+    try:
+        return triton.runtime.driver.active.get_current_target().backend
+    except BaseException:
+        return 'cpu'
+
+
+@functools.cache
+def _check_platform() -> Literal['nvidia', 'amd', 'intel', 'musa']:
+    device = get_available_device()
+    mapping = {
+        "cuda": "nvidia",
+        "hip": "amd",
+        "xpu": "intel",
+    }
+    # return the mapped value, or the original if not found
+    return mapping.get(device, device)
+
+
+# For AMD GPUs, the triton backend is 'hip', while for Nvidia GPUs, the triton backend is 'cuda'.
+# However, the torch backend is 'cuda' for both Nvidia and AMD GPUs.
+# Therefore, we need to check the triton backend to determine the actual GPU vendor.
+device = get_available_device() if get_available_device() != 'hip' else 'cuda'
+device_torch_lib = getattr(torch, device)
+device_platform = _check_platform()
+
+is_amd = (device_platform == 'amd')
+is_intel = (device_platform == 'intel')
+is_nvidia = (device_platform == 'nvidia')
+is_intel_alchemist = (is_intel
+                      and 'Intel(R) Arc(TM) A' in torch.xpu.get_device_name(0))
+is_nvidia_hopper = (is_nvidia
+                    and ('NVIDIA H' in torch.cuda.get_device_name(0)
+                         or torch.cuda.get_device_capability()[0] >= 9))
+use_cuda_graph = (is_nvidia
+                  and os.environ.get('FLA_USE_CUDA_GRAPH', '0') == '1')
+
+
+def get_all_max_shared_mem():
+    try:
+        return [
+            triton.runtime.driver.active.utils.get_device_properties(i)
+            ['max_shared_mem'] for i in range(device_torch_lib.device_count())
+        ]
+    except BaseException:
+        return [-1]
+
+
+class Backend(Enum):
+    ADA = 101376  # RTX 4090
+    AMPERE = 166912  # A100
+    HOPPER = 232448  # H100
+    DEFAULT = 102400  # Default
+
+    @classmethod
+    def get_shared_memory(cls, arch: str) -> int:
+        try:
+            return cls[arch.upper()].value
+        except KeyError:
+            return cls.DEFAULT.value
+
+
+@functools.cache
+def check_shared_mem(arch: str = "none", tensor_idx: int = 0) -> bool:
+    try:
+        device_shared_mem_list = get_all_max_shared_mem()
+        max_shared_memory = device_shared_mem_list[tensor_idx]
+        return max_shared_memory >= Backend.get_shared_memory(arch)
+    except Exception:
+        return False

vllm/model_executor/layers/fla/ops/wy_fast.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Songlin Yang, Yu Zhang
+#
+# This file contains code copied from the flash-linear-attention project.
+# The original source code was licensed under the MIT license and included
+# the following copyright notice:
+# Copyright (c) 2023-2025, Songlin Yang, Yu Zhang
+
+# ruff: noqa: E501
+from typing import Optional
+
+import torch
+
+from vllm.triton_utils import tl, triton
+
+from .index import prepare_chunk_indices
+
+
+@triton.heuristics({'IS_VARLEN': lambda args: args['cu_seqlens'] is not None})
+@triton.autotune(
+    configs=[
+        triton.Config({}, num_warps=num_warps, num_stages=num_stages)
+        for num_warps in [2, 4, 8] for num_stages in [2, 3, 4]
+    ],
+    key=['H', 'K', 'V', 'BT', 'BK', 'BV', 'IS_VARLEN'],
+)
+@triton.jit(do_not_specialize=['T'])
+def recompute_w_u_fwd_kernel(k, v, beta, w, u, A, g, cu_seqlens, chunk_indices,
+                             T, H: tl.constexpr, Hg: tl.constexpr,
+                             K: tl.constexpr, V: tl.constexpr,
+                             BT: tl.constexpr, BK: tl.constexpr,
+                             BV: tl.constexpr, IS_VARLEN: tl.constexpr):
+    i_t, i_bh = tl.program_id(0), tl.program_id(1)
+    i_b, i_h = i_bh // H, i_bh % H
+    if IS_VARLEN:
+        i_n, i_t = tl.load(chunk_indices + i_t * 2).to(
+            tl.int32), tl.load(chunk_indices + i_t * 2 + 1).to(tl.int32)
+        bos, eos = tl.load(cu_seqlens + i_n).to(
+            tl.int32), tl.load(cu_seqlens + i_n + 1).to(tl.int32)
+        T = eos - bos
+    else:
+        bos, eos = i_b * T, i_b * T + T
+    p_beta = tl.make_block_ptr(beta + bos * H + i_h, (T, ), (H, ),
+                               (i_t * BT, ), (BT, ), (0, ))
+    p_g = tl.make_block_ptr(g + (bos * H + i_h), (T, ), (H, ), (i_t * BT, ),
+                            (BT, ), (0, ))
+    p_A = tl.make_block_ptr(A + (bos * H + i_h) * BT, (T, BT), (H * BT, 1),
+                            (i_t * BT, 0), (BT, BT), (1, 0))
+    b_beta = tl.load(p_beta, boundary_check=(0, ))
+    b_A = tl.load(p_A, boundary_check=(0, 1))
+    b_g = tl.exp(tl.load(p_g, boundary_check=(0, )))
+
+    for i_v in range(tl.cdiv(V, BV)):
+        p_v = tl.make_block_ptr(v + (bos * H + i_h) * V, (T, V), (H * V, 1),
+                                (i_t * BT, i_v * BV), (BT, BV), (1, 0))
+        p_u = tl.make_block_ptr(u + (bos * H + i_h) * V, (T, V), (H * V, 1),
+                                (i_t * BT, i_v * BV), (BT, BV), (1, 0))
+        b_v = tl.load(p_v, boundary_check=(0, 1))
+        b_vb = (b_v * b_beta[:, None]).to(b_v.dtype)
+        b_u = tl.dot(b_A, b_vb, allow_tf32=False)
+        tl.store(p_u, b_u.to(p_u.dtype.element_ty), boundary_check=(0, 1))
+
+    for i_k in range(tl.cdiv(K, BK)):
+        p_k = tl.make_block_ptr(k + (bos * Hg + i_h // (H // Hg)) * K, (T, K),
+                                (Hg * K, 1), (i_t * BT, i_k * BK), (BT, BK),
+                                (1, 0))
+        p_w = tl.make_block_ptr(w + (bos * H + i_h) * K, (T, K), (H * K, 1),
+                                (i_t * BT, i_k * BK), (BT, BK), (1, 0))
+        b_k = tl.load(p_k, boundary_check=(0, 1))
+        b_kb = (b_k * b_beta[:, None] * b_g[:, None]).to(b_k.dtype)
+        b_w = tl.dot(b_A, b_kb)
+        tl.store(p_w, b_w.to(p_w.dtype.element_ty), boundary_check=(0, 1))
+
+
+def recompute_w_u_fwd(
+    k: torch.Tensor,
+    v: torch.Tensor,
+    beta: torch.Tensor,
+    g_cumsum: torch.Tensor,
+    A: torch.Tensor,
+    cu_seqlens: Optional[torch.LongTensor],
+) -> tuple[torch.Tensor, torch.Tensor]:
+    B, T, Hg, K, V = *k.shape, v.shape[-1]
+    H = v.shape[-2]
+    BT = A.shape[-1]
+
+    chunk_indices = prepare_chunk_indices(
+        cu_seqlens, BT) if cu_seqlens is not None else None
+    NT = triton.cdiv(T, BT) if cu_seqlens is None else len(chunk_indices)
+    BK = 64
+    BV = 64
+    u = torch.empty_like(v)
+    w = k.new_empty(B, T, H, K)
+    recompute_w_u_fwd_kernel[(NT, B * H)](
+        k=k,
+        v=v,
+        beta=beta,
+        w=w,
+        u=u,
+        A=A,
+        g=g_cumsum,
+        cu_seqlens=cu_seqlens,
+        chunk_indices=chunk_indices,
+        T=T,
+        H=H,
+        Hg=Hg,
+        K=K,
+        V=V,
+        BT=BT,
+        BK=BK,
+        BV=BV,
+    )
+    return w, u

vllm/triton_utils/__init__.py

@@ -7,8 +7,10 @@ from vllm.triton_utils.importing import (HAS_TRITON, TritonLanguagePlaceholder,
 if HAS_TRITON:
     import triton
     import triton.language as tl
+    import triton.language.extra.libdevice as tldevice
 else:
     triton = TritonPlaceholder()
     tl = TritonLanguagePlaceholder()
+    tldevice = TritonLanguagePlaceholder()
 
-__all__ = ["HAS_TRITON", "triton", "tl"]
+__all__ = ["HAS_TRITON", "triton", "tl", "tldevice"]