[Perf] Optimize cutlass moe problem size calculation, 5.3% E2E Throughput improvement, 2.2% TTFT improvement

csrc/ops.h

@@ -265,6 +265,11 @@ void get_cutlass_moe_mm_problem_sizes(
     const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets,
     std::optional<bool> force_swap_ab = std::nullopt);
 
+void get_cutlass_moe_mm_problem_sizes_from_expert_offsets(
+    const torch::Tensor& expert_first_token_offset,
+    torch::Tensor& problem_sizes1, torch::Tensor& problem_sizes2,
+    const int64_t n, const int64_t k, const bool swap_ab);
+
 void get_cutlass_pplx_moe_mm_data(torch::Tensor& expert_offsets,
                                   torch::Tensor& problem_sizes1,
                                   torch::Tensor& problem_sizes2,

csrc/quantization/w8a8/cutlass/moe/moe_data.cu

@@ -3,6 +3,8 @@
 #include <c10/cuda/CUDAGuard.h>
 #include <torch/all.h>
 
+#include "dispatch_utils.h"
+
 #include <iostream>
 
 constexpr uint64_t THREADS_PER_EXPERT = 512;
@@ -114,22 +116,17 @@ inline void launch_compute_problem_sizes(const torch::Tensor& topk_ids,
                                          const bool swap_ab) {
   int num_threads = min(THREADS_PER_EXPERT, topk_ids.numel());
 
-  const int32_t* topk_ptr = static_cast<const int32_t*>(topk_ids.data_ptr());
-  int32_t* ps1_ptr = static_cast<int32_t*>(problem_sizes1.data_ptr());
-  int32_t* ps2_ptr = static_cast<int32_t*>(problem_sizes2.data_ptr());
-  int32_t* atomic_ptr = static_cast<int32_t*>(atomic_buffer.data_ptr());
+  auto const* topk_ptr = topk_ids.data_ptr<int32_t>();
+  auto* ps1_ptr = problem_sizes1.data_ptr<int32_t>();
+  auto* ps2_ptr = problem_sizes2.data_ptr<int32_t>();
+  auto* atomic_ptr = atomic_buffer.data_ptr<int32_t>();
 
-  if (swap_ab) {
-    compute_problem_sizes<true><<<num_experts, num_threads, 0, stream>>>(
+  VLLM_DISPATCH_BOOL(swap_ab, SwapAB, [&] {
+    compute_problem_sizes<SwapAB><<<num_experts, num_threads, 0, stream>>>(
         topk_ptr, ps1_ptr, ps2_ptr, atomic_ptr,
         static_cast<int>(topk_ids.numel()), static_cast<int>(n),
         static_cast<int>(k));
-  } else {
-    compute_problem_sizes<false><<<num_experts, num_threads, 0, stream>>>(
-        topk_ptr, ps1_ptr, ps2_ptr, atomic_ptr,
-        static_cast<int>(topk_ids.numel()), static_cast<int>(n),
-        static_cast<int>(k));
-  }
+  });
 }
 }  // namespace
 
@@ -153,6 +150,93 @@ void get_cutlass_moe_mm_problem_sizes_caller(
                                may_swap_ab);
 }
 
+template <bool SWAP_AB>
+__global__ void compute_problem_sizes_from_expert_offsets(
+    const int64_t* __restrict__ expert_first_token_offset,
+    int32_t* __restrict__ problem_sizes1, int32_t* __restrict__ problem_sizes2,
+    const int num_experts, const int n, const int k) {
+  int const expert_id = blockIdx.x * blockDim.x + threadIdx.x;
+  if (expert_id >= num_experts) {
+    return;
+  }
+
+  int64_t const m64 = expert_first_token_offset[expert_id + 1] -
+                      expert_first_token_offset[expert_id];
+  int32_t const m = static_cast<int32_t>(m64);
+
+  int32_t* ps1 = problem_sizes1 + expert_id * 3;
+  int32_t* ps2 = problem_sizes2 + expert_id * 3;
+
+  if constexpr (!SWAP_AB) {
+    // [M, 2*N, K]
+    ps1[0] = m;
+    ps1[1] = 2 * n;
+    ps1[2] = k;
+    // [M, K, N]
+    ps2[0] = m;
+    ps2[1] = k;
+    ps2[2] = n;
+  } else {
+    // swap logical M/N in the problem shape
+    // [2*N, M, K]
+    ps1[0] = 2 * n;
+    ps1[1] = m;
+    ps1[2] = k;
+    // [K, M, N]
+    ps2[0] = k;
+    ps2[1] = m;
+    ps2[2] = n;
+  }
+}
+
+void get_cutlass_moe_mm_problem_sizes_from_expert_offsets_caller(
+    const torch::Tensor& expert_first_token_offset,
+    torch::Tensor& problem_sizes1, torch::Tensor& problem_sizes2,
+    const int64_t n, const int64_t k, const bool swap_ab) {
+  TORCH_CHECK(expert_first_token_offset.is_cuda(),
+              "expert_first_token_offset must be a CUDA tensor");
+  TORCH_CHECK(expert_first_token_offset.dtype() == torch::kInt64,
+              "expert_first_token_offset must be int64");
+
+  TORCH_CHECK(problem_sizes1.is_cuda() && problem_sizes2.is_cuda(),
+              "problem_sizes must be CUDA tensors");
+  TORCH_CHECK(problem_sizes1.dtype() == torch::kInt32 &&
+                  problem_sizes2.dtype() == torch::kInt32,
+              "problem_sizes must be int32");
+  TORCH_CHECK(problem_sizes1.is_contiguous() && problem_sizes2.is_contiguous(),
+              "problem_sizes must be contiguous");
+  TORCH_CHECK(problem_sizes1.dim() == 2 && problem_sizes2.dim() == 2,
+              "problem_sizes must be 2D tensors");
+  TORCH_CHECK(problem_sizes1.size(1) == 3 && problem_sizes2.size(1) == 3,
+              "problem_sizes second dim must be 3");
+  TORCH_CHECK(problem_sizes1.sizes() == problem_sizes2.sizes(),
+              "problem_sizes1 and problem_sizes2 must have same shape");
+
+  int64_t const num_experts64 = problem_sizes1.size(0);
+  TORCH_CHECK(expert_first_token_offset.numel() == num_experts64 + 1,
+              "expert_first_token_offset must have num_experts + 1 elements");
+  TORCH_CHECK(num_experts64 <= INT32_MAX, "num_experts must fit in int32");
+  TORCH_CHECK(n <= INT32_MAX && k <= INT32_MAX, "n and k must fit in int32");
+
+  int const num_experts = static_cast<int>(num_experts64);
+  auto stream = at::cuda::getCurrentCUDAStream(
+      expert_first_token_offset.device().index());
+
+  int const threads = (num_experts < 256) ? num_experts : 256;
+  int const blocks = (num_experts + threads - 1) / threads;
+
+  auto const* offsets_ptr = expert_first_token_offset.data_ptr<int64_t>();
+  auto* ps1_ptr = problem_sizes1.data_ptr<int32_t>();
+  auto* ps2_ptr = problem_sizes2.data_ptr<int32_t>();
+
+  VLLM_DISPATCH_BOOL(swap_ab, SwapAB, [&] {
+    compute_problem_sizes_from_expert_offsets<SwapAB>
+        <<<blocks, threads, 0, stream>>>(offsets_ptr, ps1_ptr, ps2_ptr,
+                                         num_experts, static_cast<int>(n),
+                                         static_cast<int>(k));
+  });
+}
+
 void get_cutlass_moe_mm_data_caller(
     const torch::Tensor& topk_ids, torch::Tensor& expert_offsets,
     torch::Tensor& problem_sizes1, torch::Tensor& problem_sizes2,

csrc/quantization/w8a8/cutlass/scaled_mm_entry.cu

@@ -83,6 +83,11 @@ void get_cutlass_moe_mm_problem_sizes_caller(
     const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets,
     std::optional<bool> force_swap_ab = std::nullopt);
 
+void get_cutlass_moe_mm_problem_sizes_from_expert_offsets_caller(
+    const torch::Tensor& expert_first_token_offset,
+    torch::Tensor& problem_sizes1, torch::Tensor& problem_sizes2,
+    const int64_t n, const int64_t k, const bool swap_ab);
+
 void get_cutlass_pplx_moe_mm_data_caller(torch::Tensor& expert_offsets,
                                          torch::Tensor& problem_sizes1,
                                          torch::Tensor& problem_sizes2,
@@ -322,6 +327,25 @@ void get_cutlass_moe_mm_problem_sizes(
       version_num, ". Required capability: 90, 100, or 120");
 }
 
+void get_cutlass_moe_mm_problem_sizes_from_expert_offsets(
+    const torch::Tensor& expert_first_token_offset,
+    torch::Tensor& problem_sizes1, torch::Tensor& problem_sizes2,
+    const int64_t n, const int64_t k, const bool swap_ab) {
+  int32_t version_num = get_sm_version_num();
+#if (defined ENABLE_CUTLASS_MOE_SM90 && ENABLE_CUTLASS_MOE_SM90) ||   \
+    (defined ENABLE_CUTLASS_MOE_SM100 && ENABLE_CUTLASS_MOE_SM100) || \
+    (defined ENABLE_CUTLASS_MOE_SM120 && ENABLE_CUTLASS_MOE_SM120)
+  get_cutlass_moe_mm_problem_sizes_from_expert_offsets_caller(
+      expert_first_token_offset, problem_sizes1, problem_sizes2, n, k, swap_ab);
+  return;
+#endif
+  TORCH_CHECK_NOT_IMPLEMENTED(
+      false,
+      "No compiled get_cutlass_moe_mm_problem_sizes_from_expert_offsets: "
+      "no cutlass_scaled_mm kernel for CUDA device capability: ",
+      version_num, ". Required capability: 90, 100, or 120");
+}
+
 void get_cutlass_pplx_moe_mm_data(torch::Tensor& expert_offsets,
                                   torch::Tensor& problem_sizes1,
                                   torch::Tensor& problem_sizes2,

csrc/torch_bindings.cpp

@@ -487,6 +487,17 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
   ops.impl("get_cutlass_moe_mm_problem_sizes", torch::kCUDA,
            &get_cutlass_moe_mm_problem_sizes);
 
+  // compute per-expert problem sizes from expert_first_token_offset
+  // produced by vLLM's moe_permute kernel
+  ops.def(
+      "get_cutlass_moe_mm_problem_sizes_from_expert_offsets("
+      "    Tensor expert_first_token_offset, "
+      "    Tensor! problem_sizes1, "
+      "    Tensor! problem_sizes2, "
+      "    int n, int k, bool swap_ab) -> ()");
+  ops.impl("get_cutlass_moe_mm_problem_sizes_from_expert_offsets", torch::kCUDA,
+           &get_cutlass_moe_mm_problem_sizes_from_expert_offsets);
+
   // A function that computes data required to run fused MoE with w8a8 grouped
   // GEMM and PPLX. It takes expert_num_tokens and non_zero_expert_idxs
   // as an input, and computes expert_offsets (token start indices of each

vllm/_custom_ops.py

@@ -1075,6 +1075,25 @@ def get_cutlass_moe_mm_problem_sizes(
     )
 
 
+def get_cutlass_moe_mm_problem_sizes_from_expert_offsets(
+    expert_first_token_offset: torch.Tensor,
+    problem_sizes1: torch.Tensor,
+    problem_sizes2: torch.Tensor,
+    n: int,
+    k: int,
+    swap_ab: bool,
+):
+    """Compute per-expert (M, N, K) problem sizes from expert_first_token_offset"""
+    return torch.ops._C.get_cutlass_moe_mm_problem_sizes_from_expert_offsets(
+        expert_first_token_offset,
+        problem_sizes1,
+        problem_sizes2,
+        n,
+        k,
+        swap_ab,
+    )
+
+
 def shuffle_rows(input_tensor: torch.Tensor, dst2src_map: torch.Tensor):
     """
     Shuffle and expand the input tensor according to the dst2src_map and store the result in output_tensor.

vllm/model_executor/layers/fused_moe/cutlass_moe.py

@@ -108,15 +108,7 @@ def run_cutlass_moe_fp8(
     assert global_num_experts != -1
     assert a1q_scale is not None
 
-    if expert_map is not None:
-        "Translate info from expert_map to topk_ids"
-        local_topk_ids = torch.where(
-            expert_map[topk_ids] != -1, expert_map[topk_ids], -1
-        )
-    else:
-        local_topk_ids = topk_ids
-
-    topk = local_topk_ids.size(1)
+    topk = topk_ids.size(1)
     local_E = w1.size(0)
 
     if use_batched_format:
@@ -164,12 +156,8 @@ def run_cutlass_moe_fp8(
         # during offset calculations
         expert_offsets = expert_offsets.to(torch.int64)
     else:
-        problem_sizes1 = torch.empty(
-            (global_num_experts, 3), dtype=torch.int32, device=device
-        )
-        problem_sizes2 = torch.empty(
-            (global_num_experts, 3), dtype=torch.int32, device=device
-        )
+        problem_sizes1 = torch.empty((local_E, 3), dtype=torch.int32, device=device)
+        problem_sizes2 = torch.empty((local_E, 3), dtype=torch.int32, device=device)
 
         num_expert = global_num_experts if expert_map is None else expert_map.size(0)
         # permuted a1q reuses workspace2
@@ -182,11 +170,12 @@ def run_cutlass_moe_fp8(
             expert_map,
             permuted_hidden_states=a1q_perm,
         )
-        expert_offsets = expert_first_token_offset[:-1]
-
-        ops.get_cutlass_moe_mm_problem_sizes(
-            local_topk_ids, problem_sizes1, problem_sizes2, global_num_experts, N, K
+        # swap_ab is a CUTLASS grouped-GEMM optimization (M <= 64 reduces padding).
+        swap_ab = a1q.size(0) <= 64
+        ops.get_cutlass_moe_mm_problem_sizes_from_expert_offsets(
+            expert_first_token_offset, problem_sizes1, problem_sizes2, N, K, swap_ab
         )
+        expert_offsets = expert_first_token_offset[:-1]
 
     if not per_act_token and (expert_map is not None or use_batched_format):
         # this is necessary to avoid imprecise scale calculation caused by
@@ -240,9 +229,7 @@ def run_cutlass_moe_fp8(
             permuted_hidden_states=mm2_out,
             topk_weights=topk_weights,
             inv_permuted_idx=inv_perm,
-            expert_first_token_offset=(
-                expert_first_token_offset if expert_map is not None else None
-            ),
+            expert_first_token_offset=expert_first_token_offset,
         )
 
 
@@ -772,15 +759,7 @@ def run_cutlass_moe_w4a8_fp8(
         f"w1 hidden size mismatch: got {w1.size(2) * 8}, expected {K=}"
     )
 
-    # Translate info from expert_map to topk_ids
-    if expert_map is not None:
-        local_topk_ids = torch.where(
-            expert_map[topk_ids] != -1, expert_map[topk_ids], -1
-        )
-    else:
-        local_topk_ids = topk_ids
-
-    topk = local_topk_ids.size(1)
+    topk = topk_ids.size(1)
     a1q_perm = _resize_cache(workspace2.view(dtype=torch.float8_e4m3fn), (M * topk, K))
     mm1_out = _resize_cache(workspace13, (M * topk, N * 2))
     act_out = _resize_cache(workspace2, (M * topk, N))
@@ -790,12 +769,8 @@ def run_cutlass_moe_w4a8_fp8(
     )
     mm2_out = _resize_cache(workspace2, (M * topk, K))
 
-    problem_sizes1 = torch.empty(
-        (global_num_experts, 3), dtype=torch.int32, device=device
-    )
-    problem_sizes2 = torch.empty(
-        (global_num_experts, 3), dtype=torch.int32, device=device
-    )
+    problem_sizes1 = torch.empty((local_E, 3), dtype=torch.int32, device=device)
+    problem_sizes2 = torch.empty((local_E, 3), dtype=torch.int32, device=device)
 
     num_expert = global_num_experts if expert_map is None else expert_map.size(0)
     # permuted a1q reuses workspace2
@@ -808,18 +783,11 @@ def run_cutlass_moe_w4a8_fp8(
         expert_map,
         permuted_hidden_states=a1q_perm,
     )
-    expert_offsets = expert_first_token_offset[:-1]
-
-    # For RS gemm SwapAB is always enabled (swap logical M, N in the problem shape)
-    ops.get_cutlass_moe_mm_problem_sizes(
-        local_topk_ids,
-        problem_sizes1,
-        problem_sizes2,
-        global_num_experts,
-        N,
-        K,
-        force_swap_ab=True,
+    # for RS gemm SwapAB is always enabled (swap logical M, N in the problem shape).
+    ops.get_cutlass_moe_mm_problem_sizes_from_expert_offsets(
+        expert_first_token_offset, problem_sizes1, problem_sizes2, N, K, True
     )
+    expert_offsets = expert_first_token_offset[:-1]
 
     ops.cutlass_w4a8_moe_mm(
         mm1_out,
@@ -866,9 +834,7 @@ def run_cutlass_moe_w4a8_fp8(
         permuted_hidden_states=mm2_out,
         topk_weights=topk_weights,
         inv_permuted_idx=inv_perm,
-        expert_first_token_offset=(
-            expert_first_token_offset if expert_map is not None else None
-        ),
+        expert_first_token_offset=expert_first_token_offset,
     )