[Mamba] Flashinfer selective_state_update (#36162)

Signed-off-by: Roi Koren <roik@nvidia.com>

tests/evals/gsm8k/configs/Nemotron-3-Super-120B-A12B-BF16.yaml

@@ -8,4 +8,5 @@ server_args: >-
   --max-model-len 4096
   --tensor-parallel-size 8
   --enable-expert-parallel
+  --mamba-backend flashinfer
   --speculative-config '{"method":"mtp","num_speculative_tokens":5}'

tests/evals/gsm8k/configs/Nemotron-3-Super-120B-A12B-NVFP4.yaml

@@ -8,4 +8,5 @@ server_args: >-
   --max-model-len 4096
   --tensor-parallel-size 2
   --enable-expert-parallel
+  --mamba-backend flashinfer
   --speculative-config '{"method":"mtp","num_speculative_tokens":5}'

tests/kernels/mamba/test_ssu_dispatch.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+import torch
+
+from vllm.config.mamba import MambaBackendEnum, MambaConfig
+from vllm.model_executor.layers.mamba.ops.ssu_dispatch import (
+    FlashInferSSUBackend,
+    TritonSSUBackend,
+    get_mamba_ssu_backend,
+    initialize_mamba_ssu_backend,
+    selective_state_update,
+)
+from vllm.utils.torch_utils import set_random_seed
+
+try:
+    import flashinfer.mamba  # noqa: F401
+
+    HAS_FLASHINFER = True
+except ImportError:
+    HAS_FLASHINFER = False
+
+
+def test_default_backend_is_triton():
+    initialize_mamba_ssu_backend(MambaConfig())
+    backend = get_mamba_ssu_backend()
+    assert isinstance(backend, TritonSSUBackend)
+    assert backend.name == "triton"
+
+
+def test_explicit_triton_backend():
+    initialize_mamba_ssu_backend(MambaConfig(backend=MambaBackendEnum.TRITON))
+    backend = get_mamba_ssu_backend()
+    assert isinstance(backend, TritonSSUBackend)
+
+
+@pytest.mark.skipif(not HAS_FLASHINFER, reason="flashinfer not installed")
+def test_flashinfer_backend_init():
+    initialize_mamba_ssu_backend(MambaConfig(backend=MambaBackendEnum.FLASHINFER))
+    backend = get_mamba_ssu_backend()
+    assert isinstance(backend, FlashInferSSUBackend)
+    assert backend.name == "flashinfer"
+
+
+def test_uninitialized_backend_raises():
+    import vllm.model_executor.layers.mamba.ops.ssu_dispatch as mod
+
+    old = mod._mamba_ssu_backend
+    mod._mamba_ssu_backend = None
+    with pytest.raises(RuntimeError, match="not been initialized"):
+        get_mamba_ssu_backend()
+    mod._mamba_ssu_backend = old
+
+
+@pytest.mark.skipif(HAS_FLASHINFER, reason="flashinfer is installed")
+def test_flashinfer_import_error():
+    with pytest.raises(ImportError, match="FlashInfer is required"):
+        FlashInferSSUBackend(MambaConfig())
+
+
+def test_triton_basic_call():
+    set_random_seed(0)
+    initialize_mamba_ssu_backend(MambaConfig(backend=MambaBackendEnum.TRITON))
+    device = "cuda"
+    batch_size = 2
+    dim = 64
+    dstate = 16
+
+    state = torch.randn(batch_size, dim, dstate, device=device)
+    x = torch.randn(batch_size, dim, device=device)
+    out = torch.empty_like(x)
+    dt = torch.randn(batch_size, dim, device=device)
+    dt_bias = torch.rand(dim, device=device) - 4.0
+    A = -torch.rand(dim, dstate, device=device)
+    B = torch.randn(batch_size, dstate, device=device)
+    C = torch.randn(batch_size, dstate, device=device)
+    D = torch.randn(dim, device=device)
+
+    selective_state_update(
+        state,
+        x,
+        dt,
+        A,
+        B,
+        C,
+        D=D,
+        dt_bias=dt_bias,
+        dt_softplus=True,
+        out=out,
+    )
+    assert not torch.isnan(out).any()

vllm/config/__init__.py

@@ -16,6 +16,7 @@ from vllm.config.kv_events import KVEventsConfig
 from vllm.config.kv_transfer import KVTransferConfig
 from vllm.config.load import LoadConfig
 from vllm.config.lora import LoRAConfig
+from vllm.config.mamba import MambaConfig
 from vllm.config.model import (
     ModelConfig,
     iter_architecture_defaults,
@@ -83,6 +84,8 @@ __all__ = [
     "LoadConfig",
     # From vllm.config.lora
     "LoRAConfig",
+    # From vllm.config.mamba
+    "MambaConfig",
     # From vllm.config.model
     "ModelConfig",
     "iter_architecture_defaults",

vllm/config/cache.py

@@ -123,14 +123,6 @@ class CacheConfig:
     - "align": only cache the mamba state of the last token of each scheduler step and
            when the token is at position i * block_size.
     """
-    enable_mamba_cache_stochastic_rounding: bool = False
-    """Enable stochastic rounding when writing SSM state to fp16 cache.
-    Uses random bits to unbias the rounding error, which can improve
-    numerical stability for long sequences."""
-    mamba_cache_philox_rounds: int = 0
-    """Number of Philox PRNG rounds for stochastic rounding random number
-    generation. 0 uses the Triton default. Higher values improve randomness
-    quality at the cost of compute."""
 
     # Will be set after profiling.
     num_gpu_blocks: int | None = field(default=None, init=False)
@@ -258,29 +250,3 @@ class CacheConfig:
                 str(cache_dtype),
             )
         return cache_dtype
-
-    def __post_init__(self):
-        if self.enable_mamba_cache_stochastic_rounding:
-            from vllm.platforms import current_platform
-
-            if not current_platform.is_cuda():
-                raise ValueError(
-                    "Stochastic rounding for Mamba cache is only supported "
-                    "on NVIDIA CUDA platforms. Please do not specify  "
-                    "`--enable-mamba-cache-stochastic-rounding`."
-                )
-            if not current_platform.is_device_capability_family(100):
-                raise ValueError(
-                    "Stochastic rounding for Mamba cache requires compute "
-                    "capability 10.0 (data center Blackwell). The `cvt.rs` PTX "
-                    "instruction is not supported on your GPU. Please do not specify "
-                    "`--enable-mamba-cache-stochastic-rounding`."
-                )
-            if self.mamba_ssm_cache_dtype != "float16":
-                raise ValueError(
-                    "Stochastic rounding for Mamba cache requires "
-                    "the SSM cache to be float16. Please set it explicitly, "
-                    "by specifying `--mamba-ssm-cache-dtype float16`, or disable "
-                    "stochastic rounding by not specifying "
-                    "`--enable-mamba-cache-stochastic-rounding`."
-                )

vllm/config/mamba.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from enum import Enum, EnumMeta
+from typing import Any
+
+from pydantic import field_validator
+
+from vllm.config.utils import config
+
+
+class _MambaBackendEnumMeta(EnumMeta):
+    """Metaclass for MambaBackendEnum to provide better error messages."""
+
+    def __getitem__(cls, name: str):
+        try:
+            return super().__getitem__(name)
+        except KeyError:
+            valid = ", ".join(cls.__members__.keys())
+            raise ValueError(
+                f"Unknown Mamba SSU backend: '{name}'. Valid options are: {valid}"
+            ) from None
+
+
+class MambaBackendEnum(Enum, metaclass=_MambaBackendEnumMeta):
+    """Enumeration of supported Mamba SSU (selective state update) backends."""
+
+    TRITON = "triton"
+    FLASHINFER = "flashinfer"
+
+
+@config
+class MambaConfig:
+    """Configuration for Mamba SSM backends."""
+
+    backend: MambaBackendEnum = MambaBackendEnum.TRITON
+    """Mamba SSU backend to use."""
+
+    enable_stochastic_rounding: bool = False
+    """Enable stochastic rounding when writing SSM state to fp16 cache.
+    Uses random bits to unbias the rounding error, which can improve
+    numerical stability for long sequences."""
+    stochastic_rounding_philox_rounds: int = 0
+    """Number of Philox PRNG rounds for stochastic rounding random number
+    generation. 0 uses the Triton default. Higher values improve randomness
+    quality at the cost of compute."""
+
+    @field_validator("backend", mode="before")
+    @classmethod
+    def validate_backend_before(cls, value: Any) -> Any:
+        """Enable parsing of the `backend` enum type from string."""
+        if isinstance(value, str):
+            return MambaBackendEnum[value.upper()]
+        return value
+
+    def __post_init__(self):
+        if self.enable_stochastic_rounding:
+            from vllm.platforms import current_platform
+
+            if not current_platform.is_cuda():
+                raise ValueError(
+                    "Stochastic rounding for Mamba cache is only supported "
+                    "on NVIDIA CUDA platforms. Please do not specify  "
+                    "`--enable-mamba-cache-stochastic-rounding`."
+                )
+            if (
+                self.backend == MambaBackendEnum.TRITON
+                and not current_platform.is_device_capability_family(100)
+            ):
+                raise ValueError(
+                    "Stochastic rounding for Mamba cache with triton backend requires "
+                    "compute capability 10.0 (data center Blackwell). The `cvt.rs` "
+                    "PTX instruction is not supported on your GPU. Please do not "
+                    "specify `--enable-mamba-cache-stochastic-rounding`, "
+                    "or set `--mamba-backend flashinfer`."
+                )

vllm/config/vllm.py

@@ -37,6 +37,7 @@ from .kv_events import KVEventsConfig
 from .kv_transfer import KVTransferConfig
 from .load import LoadConfig
 from .lora import LoRAConfig
+from .mamba import MambaConfig
 from .model import ModelConfig
 from .observability import ObservabilityConfig
 from .offload import OffloadConfig
@@ -275,6 +276,8 @@ class VllmConfig:
     """Model weight offloading configuration."""
     attention_config: AttentionConfig = Field(default_factory=AttentionConfig)
     """Attention configuration."""
+    mamba_config: MambaConfig = Field(default_factory=MambaConfig)
+    """Mamba configuration."""
     kernel_config: KernelConfig = Field(default_factory=KernelConfig)
     """Kernel configuration."""
     lora_config: LoRAConfig | None = None
@@ -717,6 +720,18 @@ class VllmConfig:
         if self.lora_config is not None:
             self.lora_config.verify_with_model_config(self.model_config)
 
+        if (
+            self.mamba_config.enable_stochastic_rounding
+            and self.cache_config.mamba_ssm_cache_dtype != "float16"
+        ):
+            raise ValueError(
+                "Stochastic rounding for Mamba cache requires "
+                "the SSM cache to be float16. Please set it explicitly, "
+                "by specifying `--mamba-ssm-cache-dtype float16`, or disable "
+                "stochastic rounding by not specifying "
+                "`--enable-mamba-cache-stochastic-rounding`."
+            )
+
         if self.quant_config is None and self.model_config is not None:
             self.quant_config = VllmConfig._get_quantization_config(
                 self.model_config, self.load_config

vllm/engine/arg_utils.py

@@ -45,6 +45,7 @@ from vllm.config import (
     KVTransferConfig,
     LoadConfig,
     LoRAConfig,
+    MambaConfig,
     ModelConfig,
     MultiModalConfig,
     ObservabilityConfig,
@@ -72,6 +73,7 @@ from vllm.config.cache import (
 from vllm.config.device import Device
 from vllm.config.kernel import IrOpPriorityConfig, MoEBackend
 from vllm.config.lora import MaxLoRARanks
+from vllm.config.mamba import MambaBackendEnum
 from vllm.config.model import (
     ConvertOption,
     HfOverrides,
@@ -578,6 +580,7 @@ class EngineArgs:
     pooler_config: PoolerConfig | None = ModelConfig.pooler_config
     compilation_config: CompilationConfig = get_field(VllmConfig, "compilation_config")
     attention_config: AttentionConfig = get_field(VllmConfig, "attention_config")
+    mamba_config: MambaConfig = get_field(VllmConfig, "mamba_config")
     kernel_config: KernelConfig = get_field(VllmConfig, "kernel_config")
     enable_flashinfer_autotune: bool = get_field(
         KernelConfig, "enable_flashinfer_autotune"
@@ -610,10 +613,12 @@ class EngineArgs:
     mamba_ssm_cache_dtype: MambaDType = CacheConfig.mamba_ssm_cache_dtype
     mamba_block_size: int | None = get_field(CacheConfig, "mamba_block_size")
     mamba_cache_mode: MambaCacheMode = CacheConfig.mamba_cache_mode
+
+    mamba_backend: MambaBackendEnum = MambaBackendEnum.TRITON
     enable_mamba_cache_stochastic_rounding: bool = (
-        CacheConfig.enable_mamba_cache_stochastic_rounding
+        MambaConfig.enable_stochastic_rounding
     )
-    mamba_cache_philox_rounds: int = CacheConfig.mamba_cache_philox_rounds
+    mamba_cache_philox_rounds: int = MambaConfig.stochastic_rounding_philox_rounds
 
     additional_config: dict[str, Any] = get_field(VllmConfig, "additional_config")
 
@@ -655,6 +660,8 @@ class EngineArgs:
             self.compilation_config = CompilationConfig(**self.compilation_config)
         if isinstance(self.attention_config, dict):
             self.attention_config = AttentionConfig(**self.attention_config)
+        if isinstance(self.mamba_config, dict):
+            self.mamba_config = MambaConfig(**self.mamba_config)
         if isinstance(self.kernel_config, dict):
             self.kernel_config = KernelConfig(**self.kernel_config)
         if isinstance(self.eplb_config, dict):
@@ -825,6 +832,22 @@ class EngineArgs:
             "--attention-backend", **attention_kwargs["backend"]
         )
 
+        # Mamba arguments
+        mamba_kwargs = get_kwargs(MambaConfig)
+        mamba_group = parser.add_argument_group(
+            title="MambaConfig",
+            description=MambaConfig.__doc__,
+        )
+        mamba_group.add_argument("--mamba-backend", **mamba_kwargs["backend"])
+        mamba_group.add_argument(
+            "--enable-mamba-cache-stochastic-rounding",
+            **mamba_kwargs["enable_stochastic_rounding"],
+        )
+        mamba_group.add_argument(
+            "--mamba-cache-philox-rounds",
+            **mamba_kwargs["stochastic_rounding_philox_rounds"],
+        )
+
         # Structured outputs arguments
         structured_outputs_kwargs = get_kwargs(StructuredOutputsConfig)
         structured_outputs_group = parser.add_argument_group(
@@ -1050,13 +1073,6 @@ class EngineArgs:
         cache_group.add_argument(
             "--mamba-cache-mode", **cache_kwargs["mamba_cache_mode"]
         )
-        cache_group.add_argument(
-            "--enable-mamba-cache-stochastic-rounding",
-            **cache_kwargs["enable_mamba_cache_stochastic_rounding"],
-        )
-        cache_group.add_argument(
-            "--mamba-cache-philox-rounds", **cache_kwargs["mamba_cache_philox_rounds"]
-        )
         cache_group.add_argument(
             "--kv-offloading-size", **cache_kwargs["kv_offloading_size"]
         )
@@ -1622,8 +1638,6 @@ class EngineArgs:
             mamba_ssm_cache_dtype=self.mamba_ssm_cache_dtype,
             mamba_block_size=self.mamba_block_size,
             mamba_cache_mode=self.mamba_cache_mode,
-            enable_mamba_cache_stochastic_rounding=self.enable_mamba_cache_stochastic_rounding,
-            mamba_cache_philox_rounds=self.mamba_cache_philox_rounds,
             kv_offloading_size=self.kv_offloading_size,
             kv_offloading_backend=self.kv_offloading_backend,
         )
@@ -1934,6 +1948,22 @@ class EngineArgs:
                 self.attention_backend
             )
 
+        # Mamba config overrides
+        mamba_config = copy.deepcopy(self.mamba_config)
+        # Convert string to enum if needed (CLI parsing returns a string)
+        if isinstance(self.mamba_backend, str):
+            mamba_config.backend = MambaBackendEnum[self.mamba_backend.upper()]
+        else:
+            mamba_config.backend = self.mamba_backend
+        if self.enable_mamba_cache_stochastic_rounding:
+            mamba_config.enable_stochastic_rounding = (
+                self.enable_mamba_cache_stochastic_rounding
+            )
+        if self.mamba_cache_philox_rounds:
+            mamba_config.stochastic_rounding_philox_rounds = (
+                self.mamba_cache_philox_rounds
+            )
+
         # Kernel config overrides
         kernel_config = copy.deepcopy(self.kernel_config)
         if self.enable_flashinfer_autotune is not None:
@@ -2032,6 +2062,7 @@ class EngineArgs:
             load_config=load_config,
             offload_config=offload_config,
             attention_config=attention_config,
+            mamba_config=mamba_config,
             kernel_config=kernel_config,
             lora_config=lora_config,
             speculative_config=speculative_config,

vllm/model_executor/layers/mamba/mamba_mixer.py

@@ -30,10 +30,8 @@ from vllm.model_executor.layers.mamba.ops.causal_conv1d import (
     causal_conv1d_fn,
     causal_conv1d_update,
 )
-from vllm.model_executor.layers.mamba.ops.mamba_ssm import (
-    selective_scan_fn,
-    selective_state_update,
-)
+from vllm.model_executor.layers.mamba.ops.mamba_ssm import selective_scan_fn
+from vllm.model_executor.layers.mamba.ops.ssu_dispatch import selective_state_update
 from vllm.model_executor.utils import set_weight_attrs
 from vllm.platforms import current_platform
 from vllm.utils.torch_utils import (
@@ -431,14 +429,12 @@ class MambaMixer(MambaBase, PluggableLayer):
                 B_d,
                 C_d,
                 self.D,
-                gate_d.transpose(0, 1),
                 time_proj_bias,
+                z=gate_d.transpose(0, 1),
                 dt_softplus=True,
                 state_batch_indices=state_indices_tensor_d_input,
                 dst_state_batch_indices=state_indices_tensor_d_output,
                 out=scan_outputs_d,
-                enable_stochastic_rounding=self.cache_config.enable_mamba_cache_stochastic_rounding,
-                cache_philox_rounds=self.cache_config.mamba_cache_philox_rounds,
             )
             scan_outputs_d = scan_outputs_d.transpose(0, 1)
 

vllm/model_executor/layers/mamba/mamba_mixer2.py

@@ -31,10 +31,10 @@ from vllm.model_executor.layers.mamba.ops.causal_conv1d import (
     causal_conv1d_update,
 )
 from vllm.model_executor.layers.mamba.ops.layernorm_gated import rms_norm_gated
-from vllm.model_executor.layers.mamba.ops.mamba_ssm import selective_state_update
 from vllm.model_executor.layers.mamba.ops.ssd_combined import (
     mamba_chunk_scan_combined_varlen,
 )
+from vllm.model_executor.layers.mamba.ops.ssu_dispatch import selective_state_update
 from vllm.model_executor.layers.quantization import QuantizationConfig
 from vllm.model_executor.model_loader.weight_utils import (
     LoaderFunction,
@@ -890,8 +890,7 @@ class MambaMixer2(MambaBase, PluggableLayer):
                 B_d,
                 C_d,
                 D_d,
-                z=None,
-                dt_bias=dt_bias,
+                dt_bias,
                 dt_softplus=True,
                 state_batch_indices=state_indices_tensor_d_input,
                 dst_state_batch_indices=state_indices_tensor_d_output,
@@ -899,8 +898,6 @@ class MambaMixer2(MambaBase, PluggableLayer):
                 num_accepted_tokens=num_accepted_tokens,
                 cu_seqlens=query_start_loc_d,
                 is_blackwell=self.is_blackwell,
-                enable_stochastic_rounding=self.cache_config.enable_mamba_cache_stochastic_rounding,
-                cache_philox_rounds=self.cache_config.mamba_cache_philox_rounds,
             )
 
     def get_state_dtype(self) -> tuple[torch.dtype, torch.dtype]:

vllm/model_executor/layers/mamba/ops/mamba_ssm.py

@@ -323,9 +323,9 @@ def selective_state_update(
     A,
     B,
     C,
-    D=None,
+    D,
+    dt_bias,
     z=None,
-    dt_bias=None,
     dt_softplus=False,
     state_batch_indices=None,
     dst_state_batch_indices=None,
@@ -374,11 +374,11 @@ def selective_state_update(
         B = B.unsqueeze(1)
     if C.dim() == 2:
         C = C.unsqueeze(1)
-    if D is not None and D.dim() == 1:
+    if D.dim() == 1:
         D = D.unsqueeze(0)
     if z is not None and z.dim() == 2:
         z = z.unsqueeze(1)
-    if dt_bias is not None and dt_bias.dim() == 1:
+    if dt_bias.dim() == 1:
         dt_bias = dt_bias.unsqueeze(0)
     if out.dim() == 2:
         out = out.unsqueeze(1)
@@ -410,11 +410,9 @@ def selective_state_update(
     assert nheads % ngroups == 0, "nheads must be divisible by ngroups"
     assert B.shape == (batch, ngroups, dstate)
     assert C.shape == B.shape
-    if D is not None:
     assert D.shape == (nheads, dim)
     if z is not None:
         assert z.shape == x.shape
-    if dt_bias is not None:
     assert dt_bias.shape == (nheads, dim)
     if state_batch_indices is not None:
         assert state_batch_indices.shape[0] >= N
@@ -506,7 +504,8 @@ def selective_state_update(
             dt.stride(0),
             dt.stride(1),
             dt.stride(2),
-            *(dt_bias.stride(0), dt_bias.stride(1)) if dt_bias is not None else 0,
+            dt_bias.stride(0),
+            dt_bias.stride(1),
             A.stride(0),
             A.stride(1),
             A.stride(2),
@@ -516,7 +515,8 @@ def selective_state_update(
             C.stride(0),
             C.stride(1),
             C.stride(2),
-            *(D.stride(0), D.stride(1)) if D is not None else 0,
+            D.stride(0),
+            D.stride(1),
             z_strides[0],
             z_strides[1],
             z_strides[2],

vllm/model_executor/layers/mamba/ops/ssu_dispatch.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Dispatch module for Mamba selective state update (SSU) backends.
+
+Provides a unified `selective_state_update` function that dispatches to
+either the Triton or FlashInfer backend based on the configured
+`MambaBackendEnum`. Follows SGLang's dispatch pattern adapted for vLLM.
+"""
+
+from abc import ABC, abstractmethod
+
+import torch
+
+from vllm.config.mamba import MambaBackendEnum, MambaConfig
+from vllm.logger import init_logger
+from vllm.v1.attention.backends.utils import NULL_BLOCK_ID
+
+logger = init_logger(__name__)
+
+
+class MambaSSUBackend(ABC):
+    """Abstract base class for Mamba SSU backends."""
+
+    def __init__(self, mamba_config: MambaConfig):
+        self._mamba_config = mamba_config
+
+    @property
+    @abstractmethod
+    def name(self) -> str: ...
+
+    @abstractmethod
+    def __call__(
+        self,
+        state: torch.Tensor,
+        x: torch.Tensor,
+        dt: torch.Tensor,
+        A: torch.Tensor,
+        B: torch.Tensor,
+        C: torch.Tensor,
+        D: torch.Tensor,
+        dt_bias: torch.Tensor,
+        z: torch.Tensor | None = None,
+        dt_softplus: bool = False,
+        state_batch_indices: torch.Tensor | None = None,
+        dst_state_batch_indices: torch.Tensor | None = None,
+        null_block_id: int = NULL_BLOCK_ID,
+        out: torch.Tensor | None = None,
+        num_accepted_tokens: torch.Tensor | None = None,
+        cu_seqlens: torch.Tensor | None = None,
+        is_blackwell: bool = False,
+    ) -> None: ...
+
+
+class TritonSSUBackend(MambaSSUBackend):
+    """Triton-based SSU backend (vLLM's default)."""
+
+    def __init__(self, mamba_config: MambaConfig):
+        super().__init__(mamba_config)
+        from vllm.model_executor.layers.mamba.ops.mamba_ssm import (
+            selective_state_update as _triton_selective_state_update,
+        )
+
+        self._kernel = _triton_selective_state_update
+
+    @property
+    def name(self) -> str:
+        return "triton"
+
+    def __call__(
+        self,
+        state: torch.Tensor,
+        x: torch.Tensor,
+        dt: torch.Tensor,
+        A: torch.Tensor,
+        B: torch.Tensor,
+        C: torch.Tensor,
+        D: torch.Tensor,
+        dt_bias: torch.Tensor,
+        z: torch.Tensor | None = None,
+        dt_softplus: bool = False,
+        state_batch_indices: torch.Tensor | None = None,
+        dst_state_batch_indices: torch.Tensor | None = None,
+        null_block_id: int = NULL_BLOCK_ID,
+        out: torch.Tensor | None = None,
+        num_accepted_tokens: torch.Tensor | None = None,
+        cu_seqlens: torch.Tensor | None = None,
+        is_blackwell: bool = False,
+    ) -> None:
+        self._kernel(
+            state,
+            x,
+            dt,
+            A,
+            B,
+            C,
+            D=D,
+            z=z,
+            dt_bias=dt_bias,
+            dt_softplus=dt_softplus,
+            state_batch_indices=state_batch_indices,
+            dst_state_batch_indices=dst_state_batch_indices,
+            null_block_id=null_block_id,
+            out=out,
+            num_accepted_tokens=num_accepted_tokens,
+            cu_seqlens=cu_seqlens,
+            is_blackwell=is_blackwell,
+            enable_stochastic_rounding=self._mamba_config.enable_stochastic_rounding,
+            cache_philox_rounds=self._mamba_config.stochastic_rounding_philox_rounds,
+        )
+
+
+class FlashInferSSUBackend(MambaSSUBackend):
+    """FlashInfer-based SSU backend."""
+
+    def __init__(self, mamba_config: MambaConfig):
+        super().__init__(mamba_config)
+        try:
+            from flashinfer.mamba import selective_state_update as _fi_ssu
+        except ImportError as e:
+            raise ImportError(
+                "FlashInfer is required for the flashinfer Mamba SSU backend. "
+                "Please install flashinfer (>= 0.6.4): "
+                "pip install flashinfer-python"
+            ) from e
+        self._kernel = _fi_ssu
+
+    @property
+    def name(self) -> str:
+        return "flashinfer"
+
+    def __call__(
+        self,
+        state: torch.Tensor,
+        x: torch.Tensor,
+        dt: torch.Tensor,
+        A: torch.Tensor,
+        B: torch.Tensor,
+        C: torch.Tensor,
+        D: torch.Tensor,
+        dt_bias: torch.Tensor,
+        z: torch.Tensor | None = None,
+        dt_softplus: bool = False,
+        state_batch_indices: torch.Tensor | None = None,
+        dst_state_batch_indices: torch.Tensor | None = None,
+        null_block_id: int = NULL_BLOCK_ID,
+        out: torch.Tensor | None = None,
+        num_accepted_tokens: torch.Tensor | None = None,
+        cu_seqlens: torch.Tensor | None = None,
+        is_blackwell: bool = False,
+    ) -> None:
+        rand_seed = (
+            torch.randint(0, 2**32, (1,), device=state.device)
+            if self._mamba_config.enable_stochastic_rounding
+            else None
+        )
+
+        self._kernel(
+            state,
+            x,
+            dt,
+            A,
+            B,
+            C,
+            D=D,
+            z=z,
+            dt_bias=dt_bias,
+            dt_softplus=dt_softplus,
+            state_batch_indices=state_batch_indices,
+            dst_state_batch_indices=dst_state_batch_indices,
+            cu_seqlens=cu_seqlens,
+            num_accepted_tokens=num_accepted_tokens,
+            cache_steps=state_batch_indices.size(-1)
+            if cu_seqlens is not None and state_batch_indices is not None
+            else 0,
+            pad_slot_id=null_block_id,
+            out=out,
+            rand_seed=rand_seed,
+            philox_rounds=self._mamba_config.stochastic_rounding_philox_rounds or 10,
+        )
+
+
+_BACKEND_REGISTRY: dict[MambaBackendEnum, type[MambaSSUBackend]] = {
+    MambaBackendEnum.TRITON: TritonSSUBackend,
+    MambaBackendEnum.FLASHINFER: FlashInferSSUBackend,
+}
+
+_mamba_ssu_backend: MambaSSUBackend | None = None
+
+
+def initialize_mamba_ssu_backend(mamba_config: MambaConfig) -> None:
+    """Initialize the global Mamba SSU backend.
+
+    Args:
+        mamba_config: Mamba configuration.
+    """
+    global _mamba_ssu_backend
+
+    backend = mamba_config.backend
+    if backend not in _BACKEND_REGISTRY:
+        raise ValueError(
+            f"Unknown Mamba SSU backend: {backend}. "
+            f"Valid options: {list(_BACKEND_REGISTRY.keys())}"
+        )
+
+    _mamba_ssu_backend = _BACKEND_REGISTRY[backend](mamba_config)
+    logger.info("Using %s Mamba SSU backend.", _mamba_ssu_backend.name)
+
+
+def get_mamba_ssu_backend() -> MambaSSUBackend:
+    """Get the current Mamba SSU backend. Raises if not initialized."""
+    if _mamba_ssu_backend is None:
+        raise RuntimeError(
+            "Mamba SSU backend has not been initialized. "
+            "Call initialize_mamba_ssu_backend() first."
+        )
+    return _mamba_ssu_backend
+
+
+def selective_state_update(
+    state: torch.Tensor,
+    x: torch.Tensor,
+    dt: torch.Tensor,
+    A: torch.Tensor,
+    B: torch.Tensor,
+    C: torch.Tensor,
+    D: torch.Tensor,
+    dt_bias: torch.Tensor,
+    z: torch.Tensor | None = None,
+    dt_softplus: bool = False,
+    state_batch_indices: torch.Tensor | None = None,
+    dst_state_batch_indices: torch.Tensor | None = None,
+    null_block_id: int = NULL_BLOCK_ID,
+    out: torch.Tensor | None = None,
+    num_accepted_tokens: torch.Tensor | None = None,
+    cu_seqlens: torch.Tensor | None = None,
+    is_blackwell: bool = False,
+) -> None:
+    """Unified dispatch for Mamba selective state update.
+
+    Delegates to the initialized backend (Triton or FlashInfer).
+    """
+    get_mamba_ssu_backend()(
+        state,
+        x,
+        dt,
+        A,
+        B,
+        C,
+        D,
+        dt_bias,
+        z=z,
+        dt_softplus=dt_softplus,
+        state_batch_indices=state_batch_indices,
+        dst_state_batch_indices=dst_state_batch_indices,
+        null_block_id=null_block_id,
+        out=out,
+        num_accepted_tokens=num_accepted_tokens,
+        cu_seqlens=cu_seqlens,
+        is_blackwell=is_blackwell,
+    )

vllm/model_executor/models/plamo2.py

@@ -38,10 +38,10 @@ from vllm.model_executor.layers.mamba.ops.causal_conv1d import (
     causal_conv1d_fn,
     causal_conv1d_update,
 )
-from vllm.model_executor.layers.mamba.ops.mamba_ssm import selective_state_update
 from vllm.model_executor.layers.mamba.ops.ssd_combined import (
     mamba_chunk_scan_combined_varlen,
 )
+from vllm.model_executor.layers.mamba.ops.ssu_dispatch import selective_state_update
 from vllm.model_executor.layers.quantization import QuantizationConfig
 from vllm.model_executor.layers.rotary_embedding import get_rope
 from vllm.model_executor.layers.vocab_parallel_embedding import (
@@ -447,13 +447,11 @@ class Plamo2MambaMixer(MambaBase, PluggableLayer):
                 B,
                 C,
                 D,
+                dt_bias,
                 z=gate_d.reshape(num_decodes, -1, self.head_dim),
-                dt_bias=dt_bias,
                 dt_softplus=True,
                 state_batch_indices=state_indices_tensor_d,
                 out=preallocated_ssm_out_d.view(num_decodes, -1, self.head_dim),
-                enable_stochastic_rounding=self.cache_config.enable_mamba_cache_stochastic_rounding,
-                cache_philox_rounds=self.cache_config.mamba_cache_philox_rounds,
             )
 
         # 4. Final linear projection

vllm/v1/worker/gpu/model_runner.py

@@ -36,6 +36,9 @@ from vllm.distributed.parallel_state import (
 )
 from vllm.forward_context import BatchDescriptor, set_forward_context
 from vllm.logger import init_logger
+from vllm.model_executor.layers.mamba.ops.ssu_dispatch import (
+    initialize_mamba_ssu_backend,
+)
 from vllm.model_executor.model_loader import get_model_loader
 from vllm.multimodal import MULTIMODAL_REGISTRY
 from vllm.sequence import IntermediateTensors
@@ -360,6 +363,7 @@ class GPUModelRunner(LoRAModelRunnerMixin):
         self.attn_backends, self.attn_groups, attn_cg_support = init_attn_backend(
             self.kv_cache_config, self.vllm_config, self.device
         )
+        initialize_mamba_ssu_backend(self.vllm_config.mamba_config)
         cudagraph_mode = self.compilation_config.resolve_cudagraph_mode_and_sizes(
             attn_cg_support.min_cg_support,
             attn_cg_support.min_cg_attn_backend,

vllm/v1/worker/gpu_model_runner.py

@@ -56,6 +56,9 @@ from vllm.model_executor.layers.attention_layer_base import AttentionLayerBase
 from vllm.model_executor.layers.fused_moe.routed_experts_capturer import (
     RoutedExpertsCapturer,
 )
+from vllm.model_executor.layers.mamba.ops.ssu_dispatch import (
+    initialize_mamba_ssu_backend,
+)
 from vllm.model_executor.layers.rotary_embedding import (
     MRotaryEmbedding,
     XDRotaryEmbedding,
@@ -6750,6 +6753,7 @@ class GPUModelRunner(
         self.may_add_encoder_only_layers_to_kv_cache_config()
         self.maybe_add_kv_sharing_layers_to_kv_cache_groups(kv_cache_config)
         self.initialize_attn_backend(kv_cache_config, is_profiling=is_profiling)
+        initialize_mamba_ssu_backend(self.vllm_config.mamba_config)
         # The kernel block size for all KV cache groups. For example, if
         # kv_cache_manager uses block_size 256 for a given group, but the attention
         # backends for that group only supports block_size 64, we will return