[Kernels][MoE] Fix legacy_routing to use bitmatrix-based routing path (#38504)

Signed-off-by: Andreas Karatzas <akaratza@amd.com>

tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-baseline.yaml

@@ -3,4 +3,4 @@
 model_name: openai/gpt-oss-20b
 metric_threshold: 0.568
 reasoning_effort: low
-server_args: "--attention-backend ROCM_AITER_UNIFIED_ATTN"
+server_args: "--attention-backend ROCM_AITER_UNIFIED_ATTN --tensor-parallel-size 2"
\ No newline at end of file

tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-quark-mxfp4-bf16-aiter.yaml

@@ -3,6 +3,6 @@
 model_name: amd/gpt-oss-20b-w-mxfp4-a-bf16
 metric_threshold: 0.568
 reasoning_effort: low
-server_args: "--attention-backend ROCM_AITER_UNIFIED_ATTN --moe-backend aiter"
+server_args: "--attention-backend ROCM_AITER_UNIFIED_ATTN --moe-backend aiter --tokenizer openai/gpt-oss-20b --tensor-parallel-size 2"
 env:
   VLLM_ROCM_USE_AITER: "1"
\ No newline at end of file

tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-quark-mxfp4-bf16-triton.yaml

@@ -3,4 +3,4 @@
 model_name: amd/gpt-oss-20b-w-mxfp4-a-bf16
 metric_threshold: 0.568
 reasoning_effort: low
-server_args: "--attention-backend ROCM_AITER_UNIFIED_ATTN --moe-backend triton"
+server_args: "--attention-backend ROCM_AITER_UNIFIED_ATTN --moe-backend triton --tokenizer openai/gpt-oss-20b --tensor-parallel-size 2"
\ No newline at end of file

tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-quark-mxfp4-fp8-triton.yaml

@@ -3,6 +3,6 @@
 model_name: amd/gpt-oss-20b-MoE-Quant-W-MXFP4-A-FP8-KV-FP8
 metric_threshold: 0.568
 reasoning_effort: low
-server_args: "--attention-backend ROCM_AITER_UNIFIED_ATTN"
+server_args: "--attention-backend ROCM_AITER_UNIFIED_ATTN --tensor-parallel-size 2"
 env:
   VLLM_ROCM_USE_AITER: "1"
\ No newline at end of file

tests/kernels/moe/test_gpt_oss_triton_kernels.py

@@ -23,16 +23,12 @@ from triton_kernels.numerics_details.mxfp import downcast_to_mxfp, upcast_from_m
 from triton_kernels.tensor import FP4, convert_layout, wrap_torch_tensor
 from triton_kernels.tensor_details import layout
 from triton_kernels.testing import assert_close
-from triton_kernels.topk import topk as topk_fn
 
 from vllm.model_executor.layers.fused_moe.config import mxfp4_w4a16_moe_quant_config
 from vllm.model_executor.layers.fused_moe.gpt_oss_triton_kernels_moe import (
-    legacy_routing,
-    make_routing_data,
     triton_kernel_moe_forward,
 )
 from vllm.utils.math_utils import round_up
-from vllm.utils.torch_utils import set_random_seed
 
 from .utils import shuffle_weight
 
@@ -97,10 +93,18 @@ def init_compute_data(M, K, N, E, a_dtype: str, w_dtype: str, num_warps: int):
     if w_dtype != "mx4":
         pytest.skip("NYI")
     else:  # quantize to mx4
-        # careful on the padding here, the activation padding need to be
-        # multiple of 64, the actual engine is not implemented
-        w1_bottom_pad = round_up(w1_tri.shape[1], 64) - w1_tri.shape[1]
-        w1_right_pad = round_up(w1_tri.shape[2], 128) - w1_tri.shape[2]
+        # Padding alignment depends on the platform.  On CDNA4 the scale
+        # swizzle requires SCALE_K % 8 == 0 (K % 256) and
+        # SCALE_N % 32 == 0 (2*N % 512), matching the production
+        # alignment in mxfp4_round_up_hidden_size_and_intermediate_size.
+        # On CUDA (Hopper) the scale layout pads internally, so the
+        # original 64/128 alignment is sufficient.
+        if current_platform.is_rocm():
+            k_align, n2_align = 256, 512
+        else:
+            k_align, n2_align = 64, 128
+        w1_bottom_pad = round_up(w1_tri.shape[1], k_align) - w1_tri.shape[1]
+        w1_right_pad = round_up(w1_tri.shape[2], n2_align) - w1_tri.shape[2]
 
         w2_bottom_pad = w1_right_pad // 2
         w2_right_pad = w1_bottom_pad
@@ -367,52 +371,3 @@ def test_unit_shuffle():
     )
 
     assert_close(ref=out_ref, tri=out)
-
-
-@pytest.mark.parametrize("num_tokens", [2, 8, 64])
-@pytest.mark.parametrize("num_experts", [32, 128])
-@pytest.mark.parametrize("topk", [1, 4])
-@pytest.mark.parametrize("renormalize", [True, False])
-@pytest.mark.parametrize("dtype", [torch.bfloat16])
-def test_legacy_routing(
-    num_tokens: int, num_experts: int, topk: int, renormalize: bool, dtype: torch.dtype
-):
-    set_random_seed(0)
-    gating_output = torch.randn(num_tokens, num_experts, device="cuda", dtype=dtype)
-
-    sm_first = not renormalize
-    logits = gating_output
-    if sm_first:
-        logits = torch.softmax(logits, dim=-1)
-    topk_result = topk_fn(logits, topk, apply_softmax=not sm_first)
-    # topk_fn returns SparseMatrix on NVIDIA, plain tuple on ROCm.
-    if isinstance(topk_result, tuple):
-        topk_weights, topk_ids_raw, bitmatrix = topk_result
-        from triton_kernels.routing import routing_from_bitmatrix
-
-        routing_data_ref, gather_indx_ref, scatter_indx_ref = routing_from_bitmatrix(
-            bitmatrix, topk_weights, topk_ids_raw, num_experts, topk
-        )
-    else:
-        topk_ids = topk_result.indx.to(torch.long)
-        topk_weights = topk_result.vals
-        routing_data_ref, gather_indx_ref, scatter_indx_ref = make_routing_data(
-            topk_ids, topk_weights, num_experts
-        )
-
-    routing_data, gather_indx, scatter_indx = legacy_routing(
-        gating_output, topk, sm_first=sm_first
-    )
-
-    assert_close(
-        ref=gather_indx_ref.src_indx, tri=gather_indx.src_indx, maxtol=0, rmstol=0
-    )
-    assert_close(
-        ref=gather_indx_ref.dst_indx, tri=gather_indx.dst_indx, maxtol=0, rmstol=0
-    )
-    assert_close(
-        ref=scatter_indx_ref.src_indx, tri=scatter_indx.src_indx, maxtol=0, rmstol=0
-    )
-    assert_close(
-        ref=scatter_indx_ref.dst_indx, tri=scatter_indx.dst_indx, maxtol=0, rmstol=0
-    )

tests/kernels/quantization/test_mxfp4_triton_ep.py

@@ -4,12 +4,9 @@
 Tests that triton_kernel_moe_forward correctly applies expert_map
 remapping when expert parallelism (EP) is enabled.
 
-Previously, legacy_routing was always used and it produced routing data
-with global expert IDs that didn't correspond to local weight indices,
-causing illegal memory access with EP.  The fix splits routing: when
-expert_map is provided, topk selection is performed first, expert_map is
-applied to remap global→local IDs, and make_routing_data builds routing
-structures from the local IDs.
+Both EP and non-EP paths use topk + make_routing_data. When expert_map
+is provided, global expert IDs are remapped to local IDs before building
+routing structures.
 """
 
 from unittest.mock import MagicMock, patch
@@ -24,21 +21,15 @@ class TestTritonMoeForwardExpertMap:
 
     @pytest.mark.parametrize("expert_map_present", [False, True])
     def test_routing_path_selection(self, expert_map_present):
-        """Verify that the EP-aware routing path is taken when expert_map
-        is present, and the legacy_routing path is taken otherwise."""
+        """Verify that both EP and non-EP paths use topk + make_routing_data,
+        and that expert_map remapping is applied when present."""
 
         device = "cuda" if torch.cuda.is_available() else "cpu"
-        # This is a structural test: we mock the routing functions to
-        # verify the correct path is exercised.
         mock_expert_map = (
             torch.tensor([0, -1, 1, -1], device=device) if expert_map_present else None
         )
 
         with (
-            patch(
-                "vllm.model_executor.layers.fused_moe."
-                "gpt_oss_triton_kernels_moe.legacy_routing"
-            ) as mock_legacy,
             patch("triton_kernels.topk.topk") as mock_topk,
             patch(
                 "vllm.model_executor.layers.fused_moe."
@@ -53,12 +44,10 @@ class TestTritonMoeForwardExpertMap:
                 triton_kernel_moe_forward,
             )
 
-            # Set up return values
             mock_routing_data = MagicMock()
             mock_gather = MagicMock()
             mock_scatter = MagicMock()
 
-            if expert_map_present:
             sparse_result = MagicMock()
             sparse_result.indx = torch.tensor([[0, 2]], dtype=torch.int32)
             sparse_result.vals = torch.tensor([[0.6, 0.4]])
@@ -68,12 +57,6 @@ class TestTritonMoeForwardExpertMap:
                 mock_gather,
                 mock_scatter,
             )
-            else:
-                mock_legacy.return_value = (
-                    mock_routing_data,
-                    mock_gather,
-                    mock_scatter,
-                )
 
             mock_fused_experts.return_value = torch.zeros((1, 8), device=device)
 
@@ -92,20 +75,14 @@ class TestTritonMoeForwardExpertMap:
                 expert_map=mock_expert_map,
             )
 
-            if expert_map_present:
-                # EP path: should use topk + make_routing_data, NOT
-                # legacy_routing
+            # Both paths use topk + make_routing_data
             mock_topk.assert_called_once()
             mock_make_routing.assert_called_once()
-                mock_legacy.assert_not_called()
+
+            if expert_map_present:
                 # expert_map should be None in the fused_experts call
                 # (already applied)
                 call_kwargs = mock_fused_experts.call_args
                 assert call_kwargs[1].get("expert_map") is None or (
                     len(call_kwargs[0]) > 0
                 )
-            else:
-                # Non-EP path: should use legacy_routing
-                mock_legacy.assert_called_once()
-                mock_topk.assert_not_called()
-                mock_make_routing.assert_not_called()

vllm/model_executor/layers/fused_moe/gpt_oss_triton_kernels_moe.py

@@ -47,7 +47,6 @@ if has_triton_kernels():
             BIT,
             Bitmatrix,
         )
-        from triton_kernels.topk import topk
 
         try:
             from triton_kernels.tensor import (
@@ -89,6 +88,7 @@ def pack_bitmatrix(
     offsets = offsets_m[:, None] * n_expts_act + offsets_k[None, :]
     mask = (offsets_m < n_rows)[:, None] & (offsets_k < n_expts_act)[None, :]
     indices = tl.load(topk_ids + offsets, mask=mask, other=-1)
+    valid = indices >= 0
     div = indices // 32
     rem = indices % 32
     one = tl.cast(1, tl.uint32)
@@ -99,8 +99,13 @@ def pack_bitmatrix(
         offs = tl.arange(0, BLOCK_SIZE_K // 32) + i * (BLOCK_SIZE_K // 32)
         # All topks that need to go into this column has the correct bit set.
         # Other bits are 0. x is a 2D tensor.
+        # Guard with `valid` to prevent negative indices from producing
+        # spurious bits (on HIP, -1 // 32 == 0 and 1 << (-1 % 32) sets
+        # bit 31).
         x = tl.where(
-            div[:, :, None] == offs[None, None, :], (one << rem)[:, :, None], 0
+            valid[:, :, None] & (div[:, :, None] == offs[None, None, :]),
+            (one << rem)[:, :, None],
+            0,
         )
         # Reduce x to get a single int32_t bitpack.
         y = tl.reduce_or(x, axis=1)
@@ -108,93 +113,6 @@ def pack_bitmatrix(
         tl.store(bitmatrix_ptrs, y, mask=offsets_m[:, None] < n_rows)
 
 
-def legacy_routing_from_bitmatrix(
-    bitmatrix: "Bitmatrix",
-    expt_scal: torch.Tensor,
-    expt_indx: torch.Tensor,
-    n_expts_tot: int,
-    n_expts_act: int,
-) -> tuple["RoutingData", "GatherIndx", "ScatterIndx"]:
-    """
-    Replacement for the removed triton_kernels.routing.routing_from_bitmatrix.
-    Creates routing data from a bitmatrix representation.
-    """
-    if use_legacy_triton_kernels:
-        from triton_kernels.routing import routing_from_bitmatrix
-
-        return routing_from_bitmatrix(
-            bitmatrix, expt_scal, expt_indx, n_expts_tot, n_expts_act
-        )
-    sparse_logits = SparseMatrix(indx=expt_indx, vals=expt_scal, mask=bitmatrix)
-    dispatch_indx = sparse_logits.mask_metadata.row_sorted_indx
-    combine_indx = sparse_logits.mask_metadata.col_sorted_indx
-    ragged_batch_metadata = make_ragged_tensor_metadata(
-        sparse_logits.mask_metadata.col_sum,
-        dispatch_indx.shape[0],
-    )
-    gate_scal = sparse_logits.vals.flatten()[combine_indx]
-    routing_data = RoutingData(
-        gate_scal,
-        ragged_batch_metadata.block_sizes,
-        n_expts_tot,
-        n_expts_act,
-        ragged_batch_metadata,
-    )
-    gather_idx = GatherIndx(combine_indx, dispatch_indx)
-    scatter_idx = ScatterIndx(dispatch_indx, combine_indx)
-    return routing_data, gather_idx, scatter_idx
-
-
-def legacy_routing_from_sparsematrix(
-    sparse_logits: "SparseMatrix",
-    n_expts_tot: int,
-    n_expts_act: int,
-) -> tuple["RoutingData", "GatherIndx", "ScatterIndx"]:
-    """
-    Creates routing data from a SparseMatrix representation.
-    """
-    dispatch_indx = sparse_logits.mask_metadata.row_sorted_indx
-    combine_indx = sparse_logits.mask_metadata.col_sorted_indx
-    ragged_batch_metadata = make_ragged_tensor_metadata(
-        sparse_logits.mask_metadata.col_sum,
-        dispatch_indx.shape[0],
-    )
-    gate_scal = sparse_logits.vals.flatten()[combine_indx]
-    routing_data = RoutingData(
-        gate_scal,
-        ragged_batch_metadata.block_sizes,
-        n_expts_tot,
-        n_expts_act,
-        ragged_batch_metadata,
-    )
-    gather_idx = GatherIndx(combine_indx, dispatch_indx)
-    scatter_idx = ScatterIndx(dispatch_indx, combine_indx)
-    return routing_data, gather_idx, scatter_idx
-
-
-def legacy_routing(
-    logits: torch.Tensor,
-    n_expts_act: int,
-    sm_first: bool = False,
-) -> tuple["RoutingData", "GatherIndx", "ScatterIndx"]:
-    """
-    Replacement for the removed triton_kernels.routing.routing function.
-    Computes routing data from gating logits.
-    """
-    if use_legacy_triton_kernels:
-        from triton_kernels.routing import routing
-
-        return routing(logits, n_expts_act, sm_first=sm_first)
-    if sm_first:
-        logits = torch.softmax(logits, dim=-1)
-    sparse_logits = topk(logits, n_expts_act, apply_softmax=not sm_first)
-    return legacy_routing_from_sparsematrix(
-        sparse_logits,
-        logits.shape[-1],
-        n_expts_act,
-    )
-
-
 def triton_kernel_moe_forward(
     hidden_states: torch.Tensor,
     w1,  # Tensor or triton_kernels.Tensor
@@ -241,12 +159,6 @@ def triton_kernel_moe_forward(
             unpadded_K_w2=unpadded_K_w2,
         )
 
-    if expert_map is not None:
-        # With expert parallelism, legacy_routing produces routing data
-        # using global expert IDs which don't correspond to local weight
-        # indices.  Split the routing into topk selection + expert_map
-        # remapping + local routing data construction (matching the
-        # approach used by OAITritonExperts.apply).
     from triton_kernels.topk import topk as topk_fn
 
     sm_first = not renormalize
@@ -261,6 +173,8 @@ def triton_kernel_moe_forward(
     else:
         topk_weights = topk_result.vals
         topk_ids_raw = topk_result.indx
+
+    if expert_map is not None:
         # topk_ids_raw contains global expert IDs - remap to local.
         topk_ids = expert_map[topk_ids_raw.to(torch.long)]
         local_num_experts = w1.shape[0]
@@ -271,8 +185,9 @@ def triton_kernel_moe_forward(
         effective_expert_map = None
         effective_global_num_experts = local_num_experts
     else:
-        routing_data, gather_idx, scatter_idx = legacy_routing(
-            gating_output, topk, sm_first=not renormalize
+        topk_ids = topk_ids_raw.to(torch.long)
+        routing_data, gather_idx, scatter_idx = make_routing_data(
+            topk_ids, topk_weights, gating_output.shape[-1]
         )
         effective_expert_map = expert_map
         effective_global_num_experts = global_num_experts
@@ -539,10 +454,31 @@ def make_routing_data(
 
     # matmul_ogs expects invalid topk_weights to be -1s
     topk_weights = torch.where(topk_ids == -1, -1.0, topk_weights)
-    routing_data, gather_indx, scatter_indx = legacy_routing_from_bitmatrix(
+
+    if use_legacy_triton_kernels:
+        from triton_kernels.routing import routing_from_bitmatrix
+
+        return routing_from_bitmatrix(
             bitmatrix, topk_weights, topk_ids, num_local_experts, num_topk
         )
 
+    sparse_logits = SparseMatrix(indx=topk_ids, vals=topk_weights, mask=bitmatrix)
+    dispatch_indx = sparse_logits.mask_metadata.row_sorted_indx
+    combine_indx = sparse_logits.mask_metadata.col_sorted_indx
+    ragged_batch_metadata = make_ragged_tensor_metadata(
+        sparse_logits.mask_metadata.col_sum,
+        dispatch_indx.shape[0],
+    )
+    gate_scal = sparse_logits.vals.flatten()[combine_indx]
+    routing_data = RoutingData(
+        gate_scal,
+        ragged_batch_metadata.block_sizes,
+        num_local_experts,
+        num_topk,
+        ragged_batch_metadata,
+    )
+    gather_indx = GatherIndx(combine_indx, dispatch_indx)
+    scatter_indx = ScatterIndx(dispatch_indx, combine_indx)
     return routing_data, gather_indx, scatter_indx