[Hardware][NVIDIA] FP4 MoE kernel optimization (#19110)

Signed-off-by: Chiyue Wei <chiyuew@nvidia.com>
Co-authored-by: Chiyue Wei <chiyuew@nvidia.com>

benchmarks/kernels/benchmark_cutlass_fp4_moe.py

@@ -91,7 +91,7 @@ def bench_run(
 
     score = torch.randn((m, num_experts), device=device, dtype=dtype)
 
-    topk_weights, topk_ids = fused_topk(a, score, topk, renormalize=False)
+    topk_weights, topk_ids, _ = fused_topk(a, score, topk, renormalize=False)
 
     quant_blocksize = 16
     w1_blockscale = torch.empty(

csrc/moe/moe_ops.h

@@ -31,3 +31,7 @@ torch::Tensor moe_wna16_gemm(torch::Tensor input, torch::Tensor output,
 #endif
 
 bool moe_permute_unpermute_supported();
+
+void shuffle_rows(const torch::Tensor& input_tensor,
+                  const torch::Tensor& dst2src_map,
+                  torch::Tensor& output_tensor);
\ No newline at end of file

csrc/moe/moe_permute_unpermute_op.cu

@@ -130,6 +130,62 @@ void moe_unpermute(
   });
 }
 
+template <typename T>
+__global__ void shuffleInputRowsKernel(const T* input,
+                                       const int32_t* dst2src_map, T* output,
+                                       int64_t num_src_rows,
+                                       int64_t num_dst_rows, int64_t num_cols) {
+  int64_t dest_row_idx = blockIdx.x;
+  int64_t const source_row_idx = dst2src_map[dest_row_idx];
+
+  if (blockIdx.x < num_dst_rows) {
+    // Load 128-bits per thread
+    constexpr int64_t ELEM_PER_THREAD = 128 / sizeof(T) / 8;
+    using DataElem = cutlass::Array<T, ELEM_PER_THREAD>;
+
+    // Duplicate and permute rows
+    auto const* source_row_ptr =
+        reinterpret_cast<DataElem const*>(input + source_row_idx * num_cols);
+    auto* dest_row_ptr =
+        reinterpret_cast<DataElem*>(output + dest_row_idx * num_cols);
+
+    int64_t const start_offset = threadIdx.x;
+    int64_t const stride = blockDim.x;
+    int64_t const num_elems_in_col = num_cols / ELEM_PER_THREAD;
+
+    for (int elem_index = start_offset; elem_index < num_elems_in_col;
+         elem_index += stride) {
+      dest_row_ptr[elem_index] = source_row_ptr[elem_index];
+    }
+  }
+}
+
+void shuffle_rows(const torch::Tensor& input_tensor,
+                  const torch::Tensor& dst2src_map,
+                  torch::Tensor& output_tensor) {
+  TORCH_CHECK(input_tensor.scalar_type() == output_tensor.scalar_type(),
+              "Input and output tensors must have the same data type");
+
+  auto stream = at::cuda::getCurrentCUDAStream().stream();
+  int64_t const blocks = output_tensor.size(0);
+  int64_t const threads = 256;
+  int64_t const num_dest_rows = output_tensor.size(0);
+  int64_t const num_src_rows = input_tensor.size(0);
+  int64_t const num_cols = input_tensor.size(1);
+
+  TORCH_CHECK(!(num_cols % (128 / sizeof(input_tensor.scalar_type()) / 8)),
+              "num_cols must be divisible by 128 / "
+              "sizeof(input_tensor.scalar_type()) / 8");
+
+  MOE_DISPATCH(input_tensor.scalar_type(), [&] {
+    shuffleInputRowsKernel<scalar_t><<<blocks, threads, 0, stream>>>(
+        reinterpret_cast<scalar_t*>(input_tensor.data_ptr()),
+        dst2src_map.data_ptr<int32_t>(),
+        reinterpret_cast<scalar_t*>(output_tensor.data_ptr()), num_src_rows,
+        num_dest_rows, num_cols);
+  });
+}
+
 #else
 
 void moe_permute(const torch::Tensor& input, const torch::Tensor& topk_weights,

csrc/moe/permute_unpermute_kernels/dispatch.h

@@ -19,7 +19,8 @@
   MOE_DISPATCH_CASE(at::ScalarType::Half, __VA_ARGS__)          \
   MOE_DISPATCH_CASE(at::ScalarType::BFloat16, __VA_ARGS__)      \
   MOE_DISPATCH_CASE(at::ScalarType::Float8_e5m2, __VA_ARGS__)   \
-  MOE_DISPATCH_CASE(at::ScalarType::Float8_e4m3fn, __VA_ARGS__)
+  MOE_DISPATCH_CASE(at::ScalarType::Float8_e4m3fn, __VA_ARGS__) \
+  MOE_DISPATCH_CASE(at::ScalarType::Byte, __VA_ARGS__)
 
 #define MOE_DISPATCH(TYPE, ...) \
   MOE_SWITCH(TYPE, MOE_DISPATCH_FLOAT_CASE(__VA_ARGS__))
@@ -39,6 +40,11 @@ template <>
 struct ScalarType2CudaType<at::ScalarType::BFloat16> {
   using type = __nv_bfloat16;
 };
+// uint8 for packed fp4
+template <>
+struct ScalarType2CudaType<at::ScalarType::Byte> {
+  using type = uint8_t;
+};
 
 // #if __CUDA_ARCH__ >= 890
 // fp8

csrc/moe/torch_bindings.cpp

@@ -81,6 +81,12 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, m) {
   m.def("moe_permute_unpermute_supported() -> bool");
   m.impl("moe_permute_unpermute_supported", &moe_permute_unpermute_supported);
 
+  // Row shuffle for MoE
+  m.def(
+      "shuffle_rows(Tensor input_tensor, Tensor dst2src_map, Tensor! "
+      "output_tensor) -> ()");
+  m.impl("shuffle_rows", torch::kCUDA, &shuffle_rows);
+
 #endif
 }
 

csrc/ops.h

@@ -248,7 +248,8 @@ void get_cutlass_moe_mm_data(
     const torch::Tensor& topk_ids, torch::Tensor& expert_offsets,
     torch::Tensor& problem_sizes1, torch::Tensor& problem_sizes2,
     torch::Tensor& input_permutation, torch::Tensor& output_permutation,
-    const int64_t num_experts, const int64_t n, const int64_t k);
+    const int64_t num_experts, const int64_t n, const int64_t k,
+    const std::optional<torch::Tensor>& blockscale_offsets);
 
 void cutlass_scaled_mm_azp(torch::Tensor& out, torch::Tensor const& a,
                            torch::Tensor const& b,

csrc/quantization/cutlass_w8a8/moe/moe_data.cu

@@ -45,6 +45,23 @@ __global__ void compute_expert_offsets(
   }
 }
 
+__global__ void compute_expert_blockscale_offsets(
+    const int32_t* __restrict__ problem_sizes1, int32_t* expert_offsets,
+    int32_t* blockscale_offsets, int32_t* atomic_buffer,
+    const int num_experts) {
+  int32_t tot_offset = 0;
+  int32_t tot_offset_round = 0;
+  expert_offsets[0] = 0;
+  blockscale_offsets[0] = 0;
+  for (int i = 0; i < num_experts; ++i) {
+    atomic_buffer[i] = tot_offset;
+    tot_offset += problem_sizes1[i * 3];
+    expert_offsets[i + 1] = tot_offset;
+    tot_offset_round += (problem_sizes1[i * 3] + (128 - 1)) / 128 * 128;
+    blockscale_offsets[i + 1] = tot_offset_round;
+  }
+}
+
 __global__ void compute_arg_sorts(const int* __restrict__ topk_ids,
                                   const int32_t* __restrict__ expert_offsets,
                                   int32_t* input_permutation,
@@ -77,7 +94,8 @@ void get_cutlass_moe_mm_data_caller(
     const torch::Tensor& topk_ids, torch::Tensor& expert_offsets,
     torch::Tensor& problem_sizes1, torch::Tensor& problem_sizes2,
     torch::Tensor& input_permutation, torch::Tensor& output_permutation,
-    const int64_t num_experts, const int64_t n, const int64_t k) {
+    const int64_t num_experts, const int64_t n, const int64_t k,
+    const std::optional<torch::Tensor>& blockscale_offsets) {
   auto stream = at::cuda::getCurrentCUDAStream(topk_ids.device().index());
   auto options_int32 =
       torch::TensorOptions().dtype(torch::kInt32).device(topk_ids.device());
@@ -89,10 +107,18 @@ void get_cutlass_moe_mm_data_caller(
       static_cast<int32_t*>(problem_sizes1.data_ptr()),
       static_cast<int32_t*>(problem_sizes2.data_ptr()),
       static_cast<int32_t*>(atomic_buffer.data_ptr()), topk_ids.numel(), n, k);
+  if (blockscale_offsets.has_value()) {
+    compute_expert_blockscale_offsets<<<1, 1, 0, stream>>>(
+        static_cast<const int32_t*>(problem_sizes1.data_ptr()),
+        static_cast<int32_t*>(expert_offsets.data_ptr()),
+        static_cast<int32_t*>(blockscale_offsets.value().data_ptr()),
+        static_cast<int32_t*>(atomic_buffer.data_ptr()), num_experts);
+  } else {
     compute_expert_offsets<<<1, 1, 0, stream>>>(
         static_cast<const int32_t*>(problem_sizes1.data_ptr()),
         static_cast<int32_t*>(expert_offsets.data_ptr()),
         static_cast<int32_t*>(atomic_buffer.data_ptr()), num_experts);
+  }
   compute_arg_sorts<<<num_experts, num_threads, 0, stream>>>(
       static_cast<const int32_t*>(topk_ids.data_ptr()),
       static_cast<const int32_t*>(expert_offsets.data_ptr()),

csrc/quantization/cutlass_w8a8/scaled_mm_entry.cu

@@ -54,7 +54,8 @@ void get_cutlass_moe_mm_data_caller(
     const torch::Tensor& topk_ids, torch::Tensor& expert_offsets,
     torch::Tensor& problem_sizes1, torch::Tensor& problem_sizes2,
     torch::Tensor& input_permutation, torch::Tensor& output_permutation,
-    const int64_t num_experts, const int64_t n, const int64_t k);
+    const int64_t num_experts, const int64_t n, const int64_t k,
+    const std::optional<torch::Tensor>& blockscale_offsets);
 #endif
 
 void cutlass_scaled_mm_azp_sm75(torch::Tensor& c, torch::Tensor const& a,
@@ -224,7 +225,8 @@ void get_cutlass_moe_mm_data(
     const torch::Tensor& topk_ids, torch::Tensor& expert_offsets,
     torch::Tensor& problem_sizes1, torch::Tensor& problem_sizes2,
     torch::Tensor& input_permutation, torch::Tensor& output_permutation,
-    const int64_t num_experts, const int64_t n, const int64_t k) {
+    const int64_t num_experts, const int64_t n, const int64_t k,
+    const std::optional<torch::Tensor>& blockscale_offsets) {
   // This function currently gets compiled only if we have a valid cutlass moe
   // mm to run it for.
   int32_t version_num = get_sm_version_num();
@@ -232,7 +234,8 @@ void get_cutlass_moe_mm_data(
     (defined ENABLE_SCALED_MM_SM100 && ENABLE_SCALED_MM_SM90)
   get_cutlass_moe_mm_data_caller(topk_ids, expert_offsets, problem_sizes1,
                                  problem_sizes2, input_permutation,
-                                 output_permutation, num_experts, n, k);
+                                 output_permutation, num_experts, n, k,
+                                 blockscale_offsets);
   return;
 #endif
   TORCH_CHECK_NOT_IMPLEMENTED(

csrc/torch_bindings.cpp

@@ -450,7 +450,7 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
       "                        Tensor! problem_sizes1, Tensor! problem_sizes2, "
       "                        Tensor! input_permutation, "
       "                        Tensor! output_permutation, int num_experts, "
-      "                        int n, int k) -> ()",
+      "                        int n, int k, Tensor? blockscale_offsets) -> ()",
       {stride_tag});
   ops.impl("get_cutlass_moe_mm_data", torch::kCUDA, &get_cutlass_moe_mm_data);
 

tests/kernels/moe/test_nvfp4_moe.py

@@ -80,7 +80,10 @@ def test_cutlass_fp4_moe_no_graph(m: int, n: int, k: int, e: int, topk: int,
                 w2[expert], w2_gs[expert])
 
         score = torch.randn((m, e), device="cuda", dtype=dtype)
-        topk_weights, topk_ids = fused_topk(a, score, topk, renormalize=False)
+        topk_weights, topk_ids, _ = fused_topk(a,
+                                               score,
+                                               topk,
+                                               renormalize=False)
 
         a1_gs = torch.ones((e, ), device="cuda", dtype=torch.float32)
         a2_gs = torch.ones((e, ), device="cuda", dtype=torch.float32)

vllm/_custom_ops.py

@@ -845,11 +845,16 @@ def cutlass_scaled_sparse_mm(
     return out
 
 
-def get_cutlass_moe_mm_data(
-        topk_ids: torch.Tensor, expert_offsets: torch.Tensor,
-        problem_sizes1: torch.Tensor, problem_sizes2: torch.Tensor,
-        input_permutation: torch.Tensor, output_permutation: torch.Tensor,
-        num_experts: int, n: int, k: int):
+def get_cutlass_moe_mm_data(topk_ids: torch.Tensor,
+                            expert_offsets: torch.Tensor,
+                            problem_sizes1: torch.Tensor,
+                            problem_sizes2: torch.Tensor,
+                            input_permutation: torch.Tensor,
+                            output_permutation: torch.Tensor,
+                            num_experts: int,
+                            n: int,
+                            k: int,
+                            blockscale_offsets: Optional[torch.Tensor] = None):
     """
     Prepare data necessary to perform CUTLASS grouped matrix multiplications
     used in CUTLASS-based fused MoE.
@@ -867,12 +872,31 @@ def get_cutlass_moe_mm_data(
                          before executing the MMs.
     - output_permutation: Permutation that must be used to shuffle the output
                           after executing the MMs.
+    - blockscale_offsets: Optional argument passed for fp4 moe. Indices that
+                          mark at which block scale index each expert begins
+                          its computation. The number of block scale rows
+                          computed with expert E is blockscale_offsets[E + 1] -
+                          blockscale_offsets[E]
     """
     return torch.ops._C.get_cutlass_moe_mm_data(topk_ids, expert_offsets,
                                                 problem_sizes1, problem_sizes2,
                                                 input_permutation,
                                                 output_permutation,
-                                                num_experts, n, k)
+                                                num_experts, n, k,
+                                                blockscale_offsets)
+
+
+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.
+    This is used in MoE to permute the input tensor before performing grouped matrix multiplications.
+    """
+    num_tokens_permuted = dst2src_map.shape[0]
+    output_tensor = torch.empty((num_tokens_permuted, input_tensor.shape[1]),
+                                device=input_tensor.device,
+                                dtype=input_tensor.dtype)
+    torch.ops._moe_C.shuffle_rows(input_tensor, dst2src_map, output_tensor)
+    return output_tensor
 
 
 def cutlass_moe_mm(out_tensors: torch.Tensor, a_tensors: torch.Tensor,
@@ -1124,14 +1148,12 @@ def scaled_fp4_experts_quant(
     expert_offsets: torch.Tensor,
     blockscale_offsets: torch.Tensor,
     topk: int,
-    expert_map: Optional[torch.Tensor] = None,
 ) -> tuple[torch.Tensor, torch.Tensor]:
     """
     Quantize input tensor to FP4 and return quantized tensor and scale, for
     packed MoE Inputs.
     Args:
-        input: The input tensor to be quantized to FP4
-        expert_map: The expert map tensor
+        input_tensor: The input tensor to be quantized to FP4
         input_global_scale: A scalar scaling factor for the entire tensor.
         expert_offsets: The expert offsets tensor
         blockscale_offsets: The blockscale offsets tensor
@@ -1143,14 +1165,13 @@ def scaled_fp4_experts_quant(
     assert input_tensor.ndim == 2, (
         f'input.ndim needs to be == 2, but got {input_tensor.ndim}.')
 
-    input_tensor = input_tensor[
-        expert_map] if expert_map is not None else input_tensor
-    m_numtopk, k = input_tensor.shape
     # Control the maximum number of tokens per expert supported by the
     # NVFP4 MoE Expert Quantization. This is used to prevent the kernel
     # from running out of memory. This value can also be increased to support
     # larger models.
     MAX_TOKENS_PER_EXPERT = envs.VLLM_MAX_TOKENS_PER_EXPERT_FP4_MOE
+    m_numtopk, k = input_tensor.shape
+
     assert (m_numtopk <= MAX_TOKENS_PER_EXPERT * topk), (
         f"m_numtopk must be less than MAX_TOKENS_PER_EXPERT("
         f"{MAX_TOKENS_PER_EXPERT})"

vllm/model_executor/layers/fused_moe/cutlass_moe.py

@@ -333,6 +333,7 @@ def cutlass_moe_fp4(a: torch.Tensor, a1_gscale: torch.Tensor,
     num_topk = topk_ids.shape[1]
 
     expert_offsets = torch.empty((e + 1), dtype=torch.int32, device=device)
+    blockscale_offsets = torch.empty((e + 1), dtype=torch.int32, device=device)
     # Problem size:  (num_experts, (m,2n,k))
     problem_sizes1 = torch.empty((e, 3), dtype=torch.int32, device=device)
     # Problem size:  (num_experts, (m,n,k))
@@ -344,12 +345,10 @@ def cutlass_moe_fp4(a: torch.Tensor, a1_gscale: torch.Tensor,
     # problem shapes should have [m, n, k]
     # Note that problem sizes are based on logical number of elements.
     ops.get_cutlass_moe_mm_data(topk_ids, expert_offsets, problem_sizes1,
-                                problem_sizes2, a_map, c_map, e, n, k)
+                                problem_sizes2, a_map, c_map, e, n, k,
+                                blockscale_offsets)
 
-    tokens_per_expert = problem_sizes1[:, 0]
-    rounded_tokens_per_expert = (tokens_per_expert + (128 - 1)) // 128 * 128
-    blockscale_offsets = torch.zeros(e + 1, dtype=torch.int32, device=device)
-    blockscale_offsets[1:] = torch.cumsum(rounded_tokens_per_expert, dim=0)
+    a = ops.shuffle_rows(a, a_map)
 
     rep_a_fp4, rep_a_blockscale = ops.scaled_fp4_experts_quant(
         a,
@@ -357,7 +356,7 @@ def cutlass_moe_fp4(a: torch.Tensor, a1_gscale: torch.Tensor,
         expert_offsets,
         blockscale_offsets,
         num_topk,
-        expert_map=a_map)
+    )
 
     c1 = ops.cutlass_fp4_moe_mm(rep_a_fp4, w1_fp4, rep_a_blockscale,
                                 w1_blockscale, w1_alphas, problem_sizes1,
@@ -378,6 +377,8 @@ def cutlass_moe_fp4(a: torch.Tensor, a1_gscale: torch.Tensor,
                                 w2_alphas, problem_sizes2, expert_offsets[:-1],
                                 blockscale_offsets[:-1], out_dtype, device)
     del int_fp4, int_blockscale
-    out = (c2[c_map].view(m, num_topk, k) *
+
+    c2 = ops.shuffle_rows(c2, c_map)
+    out = (c2.view(m, num_topk, k) *
            topk_weights.view(m, num_topk, 1).half()).sum(dim=1)
     return out.to(dtype=out_dtype)