[Feature] Non-contiguous Support for FP8 Quantization (vllm-project#21961)

Signed-off-by: yewentao256 <zhyanwentao@126.com>
Co-authored-by: mgoin <mgoin64@gmail.com>
Signed-off-by: Paul Pak <paulpak58@gmail.com>

Author: 2 people

csrc/quantization/fp8/common.cu

@@ -1,7 +1,8 @@
 #include "common.cuh"
 #include "dispatch_utils.h"
-
+#include "../vectorization_utils.cuh"
 #include <c10/cuda/CUDAGuard.h>
+#include <ATen/cuda/Exceptions.h>
 
 #ifndef USE_ROCM
   #include <cub/cub.cuh>
@@ -12,74 +13,127 @@
 namespace vllm {
 
 template <typename scalar_t, typename fp8_type>
-__global__ void scaled_fp8_quant_kernel(fp8_type* __restrict__ out,
-                                        const scalar_t* __restrict__ input,
-                                        const float* __restrict__ scale,
-                                        int64_t num_elems) {
-  int tid = blockDim.x * blockIdx.x + threadIdx.x;
-
-  // Invert the scale so that we can use multiplications to avoid expensive
-  // division.
-  const float inverted_scale = 1.0f / (*scale);
-  scaled_fp8_conversion_vec<scalar_t, true>(
-      out, input, inverted_scale, num_elems, tid, blockDim.x * gridDim.x);
+__global__ void scaled_fp8_quant_kernel_strided(
+    fp8_type* __restrict__ out, const scalar_t* __restrict__ input,
+    const float* __restrict__ scale, int hidden_size, int64_t in_row_stride,
+    int64_t out_row_stride) {
+  const int64_t token_idx = blockIdx.x;  // one token per block
+  const int tid = threadIdx.x;
+
+  const scalar_t* token_in = input + token_idx * in_row_stride;
+  fp8_type* token_out = out + token_idx * out_row_stride;
+
+  const float inv_scale = 1.0f / (*scale);
+
+  vectorize_with_alignment<16>(
+      token_in, token_out, hidden_size, tid, blockDim.x,
+      [=] __device__(fp8_type & dst, const scalar_t& src) {
+        dst = scaled_fp8_conversion<true, fp8_type>(static_cast<float>(src),
+                                                    inv_scale);
+      });
 }
 
 template <typename scalar_t, typename fp8_type>
-__global__ void dynamic_per_token_scaled_fp8_quant_kernel(
-    fp8_type* __restrict__ out, float* __restrict__ scale,
-    scalar_t const* __restrict__ input, float const* __restrict__ scale_ub,
-    const int hidden_size) {
-  int const tid = threadIdx.x;
-  int const token_idx = blockIdx.x;
+__global__ void segmented_max_reduction_strided(
+    float* __restrict__ scale, const scalar_t* __restrict__ input,
+    int hidden_size, int64_t in_row_stride, int64_t num_tokens) {
+  __shared__ float cache[256];
+  const int tid = threadIdx.x;
+  int64_t token_idx = blockIdx.x;
+
+  // one block per token. Guard in case gridDim.x > num_tokens.
+  if (token_idx >= num_tokens) {
+    return;
+  }
 
-  // Use int64 to avoid overflowing an int32 when calculating this offset
-  int64_t offset = static_cast<int64_t>(token_idx) * hidden_size;
-  scalar_t const* __restrict__ token_input = &input[offset];
-  fp8_type* __restrict__ token_output = &out[offset];
-
-  // For vectorization, token_input and token_output pointers need to be
-  // aligned at 32-byte and 16-byte addresses respectively.
-  bool const can_vectorize = hidden_size % 16 == 0;
-
-  float absmax_val = 0.0f;
-  if (can_vectorize) {
-    absmax_val = thread_max_vec(token_input, hidden_size, tid, blockDim.x);
-  } else {
-    for (int i = tid; i < hidden_size; i += blockDim.x) {
-      float const x = static_cast<float>(token_input[i]);
-      absmax_val = fmaxf(absmax_val, fabsf(x));
+  const scalar_t* row_ptr = input + token_idx * in_row_stride;
+
+  // each thread scans elements of the row in a strided fashion.
+  float thread_max = 0.0f;
+  for (int e = tid; e < hidden_size; e += blockDim.x) {
+    float v = fabsf(static_cast<float>(row_ptr[e]));
+    thread_max = fmaxf(thread_max, v);
+  }
+
+  cache[tid] = thread_max;
+  __syncthreads();
+
+  // parallel reduction to find row max.
+  for (int offset = blockDim.x / 2; offset > 0; offset >>= 1) {
+    if (tid < offset) {
+      cache[tid] = fmaxf(cache[tid], cache[tid + offset]);
     }
+    __syncthreads();
   }
 
+  // thread 0 updates global scale (per-tensor) atomically.
+  if (tid == 0) {
+    atomicMaxFloat(scale, cache[0] / quant_type_max_v<fp8_type>);
+  }
+}
+
+template <typename scalar_t, typename fp8_type>
+__global__ void scaled_fp8_quant_kernel_strided_dynamic(
+    fp8_type* __restrict__ out, const scalar_t* __restrict__ input,
+    const float* __restrict__ scale, int hidden_size, int64_t in_row_stride,
+    int64_t out_row_stride) {
+  const int64_t token_idx = blockIdx.x;
+  const int tid = threadIdx.x;
+
+  const scalar_t* token_in = input + token_idx * in_row_stride;
+  fp8_type* token_out = out + token_idx * out_row_stride;
+
+  const float reciprocal_scale = 1.0f / (*scale);
+  vectorize_with_alignment<16>(
+      token_in, token_out, hidden_size, tid, blockDim.x,
+      [=] __device__(fp8_type & dst, const scalar_t& src) {
+        dst = scaled_fp8_conversion<true, fp8_type>(static_cast<float>(src),
+                                                    reciprocal_scale);
+      });
+}
+
+template <typename scalar_t, typename fp8_type>
+__global__ void dynamic_per_token_scaled_fp8_quant_kernel_strided(
+    fp8_type* __restrict__ out, float* __restrict__ scale,
+    const scalar_t* __restrict__ input, const float* __restrict__ scale_ub,
+    int hidden_size, int64_t in_row_stride, int64_t out_row_stride) {
+  const int64_t token_idx = blockIdx.x;
+  const int tid = threadIdx.x;
+
+  // Use int64 to avoid overflowing an int32 when calculating this offset
+  int64_t in_offset = static_cast<int64_t>(token_idx) * in_row_stride;
+  int64_t out_offset = static_cast<int64_t>(token_idx) * out_row_stride;
+  const scalar_t* token_in = input + in_offset;
+  fp8_type* token_out = out + out_offset;
+
+  // 1) per-token absmax
+  float absmax_val = 0.f;
+  vectorize_read_with_alignment<16>(
+      token_in, hidden_size, tid, blockDim.x, [&] __device__(scalar_t v) {
+        absmax_val = fmaxf(absmax_val, fabsf(static_cast<float>(v)));
+      });
+
   using BlockReduce = cub::BlockReduce<float, 256>;
-  __shared__ typename BlockReduce::TempStorage reduceStorage;
-  float const block_absmax_val_maybe =
-      BlockReduce(reduceStorage).Reduce(absmax_val, cub::Max{}, blockDim.x);
+  __shared__ typename BlockReduce::TempStorage tmp;
+  const float block_max =
+      BlockReduce(tmp).Reduce(absmax_val, cub::Max{}, blockDim.x);
+
   __shared__ float token_scale;
   if (tid == 0) {
-    if (scale_ub) {
-      token_scale = fminf(block_absmax_val_maybe, *scale_ub);
-    } else {
-      token_scale = block_absmax_val_maybe;
-    }
-    // token scale computation
+    token_scale = scale_ub ? fminf(block_max, *scale_ub) : block_max;
     token_scale = fmaxf(token_scale / quant_type_max_v<fp8_type>,
                         min_scaling_factor<fp8_type>::val());
     scale[token_idx] = token_scale;
   }
   __syncthreads();
 
-  // Note that we don't use inverted scales so we can match FBGemm impl.
-  if (can_vectorize) {
-    scaled_fp8_conversion_vec<scalar_t, false>(
-        token_output, token_input, token_scale, hidden_size, tid, blockDim.x);
-  } else {
-    for (int i = tid; i < hidden_size; i += blockDim.x) {
-      token_output[i] = scaled_fp8_conversion<false, fp8_type>(
-          static_cast<float>(token_input[i]), token_scale);
-    }
-  }
+  // 2) quantize
+  vectorize_with_alignment<16>(
+      token_in, token_out, hidden_size, tid, blockDim.x,
+      [=] __device__(fp8_type & dst, const scalar_t& src) {
+        dst = scaled_fp8_conversion<false, fp8_type>(static_cast<float>(src),
+                                                     token_scale);
+      });
 }
 
 }  // namespace vllm
@@ -88,23 +142,31 @@ void static_scaled_fp8_quant(torch::Tensor& out,          // [..., d]
                              torch::Tensor const& input,  // [..., d]
                              torch::Tensor const& scale)  // [1]
 {
-  TORCH_CHECK(input.is_contiguous());
-  TORCH_CHECK(out.is_contiguous());
-  int const block_size = 256;
-  int const num_tokens = input.numel() / input.size(-1);
-  int const num_elems = input.numel();
-  dim3 const grid(num_tokens);
-  dim3 const block(block_size);
+  TORCH_CHECK(input.stride(-1) == 1,
+              "last dimension of input must be contiguous");
+  TORCH_CHECK(out.stride(-1) == 1,
+              "last dimension of output must be contiguous");
+
+  const int hidden_size = input.size(-1);
+  const int num_tokens = input.numel() / hidden_size;
+  const int block_size = 256;
+  dim3 grid(num_tokens);
+  dim3 block(block_size);
+
+  const int64_t in_row_stride = input.stride(-2);
+  const int64_t out_row_stride = out.stride(-2);
+
   const at::cuda::OptionalCUDAGuard device_guard(device_of(input));
   const cudaStream_t stream = at::cuda::getCurrentCUDAStream();
   VLLM_DISPATCH_FLOATING_TYPES(
       input.scalar_type(), "scaled_fp8_quant_kernel_scalar_type", [&] {
         VLLM_DISPATCH_FP8_TYPES(
             out.scalar_type(), "scaled_fp8_quant_kernel_fp8_type", [&] {
-              vllm::scaled_fp8_quant_kernel<scalar_t, fp8_t>
+              vllm::scaled_fp8_quant_kernel_strided<scalar_t, fp8_t>
                   <<<grid, block, 0, stream>>>(
                       out.data_ptr<fp8_t>(), input.data_ptr<scalar_t>(),
-                      scale.data_ptr<float>(), num_elems);
+                      scale.data_ptr<float>(), hidden_size, in_row_stride,
+                      out_row_stride);
             });
       });
 }
@@ -113,27 +175,42 @@ void dynamic_scaled_fp8_quant(torch::Tensor& out,          // [..., d]
                               torch::Tensor const& input,  // [..., d]
                               torch::Tensor& scale)        // [1]
 {
-  TORCH_CHECK(input.is_contiguous());
-  TORCH_CHECK(out.is_contiguous());
-  int const block_size = 256;
-  int const num_tokens = input.numel() / input.size(-1);
-  int const num_elems = input.numel();
-  dim3 const grid(num_tokens);
-  dim3 const block(block_size);
+  TORCH_CHECK(input.stride(-1) == 1,
+              "last dimension of input must be contiguous");
+  TORCH_CHECK(out.stride(-1) == 1,
+              "last dimension of output must be contiguous");
+
+  const int hidden_size = input.size(-1);
+  const int num_tokens = input.numel() / hidden_size;
+  const int block_size = 256;
+  dim3 grid(num_tokens);
+  dim3 block(block_size);
+
+  const int64_t in_row_stride = input.stride(-2);
+  const int64_t out_row_stride = out.stride(-2);
+
   const at::cuda::OptionalCUDAGuard device_guard(device_of(input));
   const cudaStream_t stream = at::cuda::getCurrentCUDAStream();
+
+  // scale tensor should be initialised to <=0 before reduction
+  AT_CUDA_CHECK(
+      cudaMemsetAsync(scale.data_ptr<float>(), 0, sizeof(float), stream));
+
   VLLM_DISPATCH_FLOATING_TYPES(
       input.scalar_type(), "scaled_fp8_quant_kernel_scalar_type", [&] {
         VLLM_DISPATCH_FP8_TYPES(
             out.scalar_type(), "scaled_fp8_quant_kernel_fp8_type", [&] {
-              vllm::segmented_max_reduction<scalar_t, fp8_t>
-                  <<<grid, block, 0, stream>>>(scale.data_ptr<float>(),
-                                               input.data_ptr<scalar_t>(),
-                                               num_elems);
-              vllm::scaled_fp8_quant_kernel<scalar_t, fp8_t>
+              vllm::segmented_max_reduction_strided<scalar_t, fp8_t>
+                  <<<grid, block, 0, stream>>>(
+                      scale.data_ptr<float>(), input.data_ptr<scalar_t>(),
+                      hidden_size, in_row_stride,
+                      static_cast<int64_t>(num_tokens));
+
+              vllm::scaled_fp8_quant_kernel_strided_dynamic<scalar_t, fp8_t>
                   <<<grid, block, 0, stream>>>(
                       out.data_ptr<fp8_t>(), input.data_ptr<scalar_t>(),
-                      scale.data_ptr<float>(), num_elems);
+                      scale.data_ptr<float>(), hidden_size, in_row_stride,
+                      out_row_stride);
             });
       });
 }
@@ -142,14 +219,19 @@ void dynamic_per_token_scaled_fp8_quant(
     torch::Tensor& out,          // [..., d]
     torch::Tensor const& input,  // [..., d]
     torch::Tensor& scales, std::optional<at::Tensor> const& scale_ub) {
-  TORCH_CHECK(input.is_contiguous());
-  TORCH_CHECK(out.is_contiguous());
+  TORCH_CHECK(input.stride(-1) == 1,
+              "last dimension of input must be contiguous");
+  TORCH_CHECK(out.stride(-1) == 1,
+              "last dimension of output must be contiguous");
 
-  int const hidden_size = input.size(-1);
-  int const num_tokens = input.numel() / hidden_size;
-  int const block_size = 256;
-  dim3 const grid(num_tokens);
-  dim3 const block(std::min(hidden_size, block_size));
+  const int hidden_size = input.size(-1);
+  const int num_tokens = input.numel() / hidden_size;
+  const int block_size = 256;
+  dim3 grid(num_tokens);
+  dim3 block(std::min(hidden_size, block_size));
+
+  const int64_t in_row_stride = input.stride(-2);
+  const int64_t out_row_stride = out.stride(-2);
 
   const at::cuda::OptionalCUDAGuard device_guard(device_of(input));
   const cudaStream_t stream = at::cuda::getCurrentCUDAStream();
@@ -159,13 +241,12 @@ void dynamic_per_token_scaled_fp8_quant(
         VLLM_DISPATCH_FP8_TYPES(
             out.scalar_type(),
             "dynamic_per_token_scaled_fp8_quant_kernel_fp8_type", [&] {
-              vllm::dynamic_per_token_scaled_fp8_quant_kernel<scalar_t, fp8_t>
-                  <<<grid, block, 0, stream>>>(
-                      out.data_ptr<fp8_t>(), scales.data_ptr<float>(),
-                      input.data_ptr<scalar_t>(),
-                      scale_ub.has_value() ? scale_ub->data_ptr<float>()
-                                           : nullptr,
-                      hidden_size);
+              vllm::dynamic_per_token_scaled_fp8_quant_kernel_strided<
+                  scalar_t, fp8_t><<<grid, block, 0, stream>>>(
+                  out.data_ptr<fp8_t>(), scales.data_ptr<float>(),
+                  input.data_ptr<scalar_t>(),
+                  scale_ub.has_value() ? scale_ub->data_ptr<float>() : nullptr,
+                  hidden_size, in_row_stride, out_row_stride);
             });
       });
 }