[Refactor] Reduce duplicate code in `per_token_group_quant` cuda kernels (#30496)

Signed-off-by: yewentao256 <zhyanwentao@126.com>

csrc/quantization/w8a8/fp8/per_token_group_quant.cu

@@ -22,6 +22,62 @@ __device__ __forceinline__ float GroupReduceMax(float val) {
   return val;
 }
 
+template <typename T, bool SCALE_UE8M0>
+__device__ __forceinline__ float ComputeGroupScale(
+    const T* __restrict__ group_input, T* __restrict__ smem_group,
+    const int group_size, const int lane_id, const int threads_per_group,
+    const float eps, const float max_8bit) {
+  float local_absmax = eps;
+
+  constexpr int vec_size = 16 / sizeof(T);
+
+  // copy global -> shared & compute absmax
+  auto scalar_op_cache = [&] __device__(T & dst, const T& src) {
+    float abs_v = fabsf(static_cast<float>(src));
+    local_absmax = fmaxf(local_absmax, abs_v);
+    dst = src;
+  };
+
+  vllm::vectorize_with_alignment<vec_size>(
+      group_input,        // in
+      smem_group,         // out (shared)
+      group_size,         // elements per group
+      lane_id,            // thread id
+      threads_per_group,  // stride in group
+      scalar_op_cache);   // scalar handler
+
+  local_absmax = GroupReduceMax(local_absmax);
+
+  float y_s = local_absmax / max_8bit;
+  if constexpr (SCALE_UE8M0) {
+    y_s = exp2f(ceilf(log2f(fmaxf(fabsf(y_s), 1e-10f))));
+  }
+
+  return y_s;
+}
+
+template <typename T, typename DST_DTYPE>
+__device__ __forceinline__ void QuantizeGroup(
+    const T* __restrict__ smem_group, DST_DTYPE* __restrict__ group_output,
+    const int group_size, const int lane_id, const int threads_per_group,
+    const float y_s, const float min_8bit, const float max_8bit) {
+  constexpr int vec_size = 16 / sizeof(T);
+
+  // quantize shared -> global 8-bit
+  auto scalar_op_quant = [&] __device__(DST_DTYPE & dst, const T& src) {
+    float q = fminf(fmaxf(static_cast<float>(src) / y_s, min_8bit), max_8bit);
+    dst = DST_DTYPE(q);
+  };
+
+  vllm::vectorize_with_alignment<vec_size>(
+      smem_group,         // in (shared)
+      group_output,       // out (global quant tensor)
+      group_size,         // elements
+      lane_id,            // tid
+      threads_per_group,  // stride
+      scalar_op_quant);   // scalar handler
+}
+
 template <typename T, typename DST_DTYPE, bool IS_COLUMN_MAJOR = false,
           bool SCALE_UE8M0 = false, typename scale_packed_t = float>
 __global__ void per_token_group_quant_8bit_kernel(
@@ -38,8 +94,6 @@ __global__ void per_token_group_quant_8bit_kernel(
   const int64_t global_group_id = block_group_id + local_group_id;
   const int64_t block_group_offset = global_group_id * group_size;
 
-  float local_absmax = eps;
-
   using scale_element_t = float;
   static_assert(sizeof(scale_packed_t) % sizeof(scale_element_t) == 0);
 
@@ -68,30 +122,9 @@ __global__ void per_token_group_quant_8bit_kernel(
   T* smem = reinterpret_cast<T*>(smem_raw);
   T* smem_group = smem + local_group_id * group_size;
 
-  constexpr int vec_size = 16 / sizeof(T);
-  using vec_t = vllm::vec_n_t<T, vec_size>;
-
-  // copy global -> shared & compute absmax
-  auto scalar_op_cache = [&] __device__(T & dst, const T& src) {
-    float abs_v = fabsf(static_cast<float>(src));
-    local_absmax = fmaxf(local_absmax, abs_v);
-    dst = src;
-  };
-
-  vllm::vectorize_with_alignment<vec_size>(
-      group_input,        // in
-      smem_group,         // out (shared)
-      group_size,         // elements per group
-      lane_id,            // thread id
-      threads_per_group,  // stride in group
-      scalar_op_cache);   // scalar handler
-
-  local_absmax = GroupReduceMax(local_absmax);
-
-  float y_s = local_absmax / max_8bit;
-  if constexpr (SCALE_UE8M0) {
-    y_s = exp2f(ceilf(log2f(fmaxf(fabsf(y_s), 1e-10f))));
-  }
+  const float y_s = ComputeGroupScale<T, SCALE_UE8M0>(
+      group_input, smem_group, group_size, lane_id, threads_per_group, eps,
+      max_8bit);
 
   scale_element_t y_s_quant = y_s;
 
@@ -101,19 +134,24 @@ __global__ void per_token_group_quant_8bit_kernel(
 
   __syncthreads();
 
-  // quantize shared -> global 8-bit
-  auto scalar_op_quant = [&] __device__(DST_DTYPE & dst, const T& src) {
-    float q = fminf(fmaxf(static_cast<float>(src) / y_s, min_8bit), max_8bit);
-    dst = DST_DTYPE(q);
-  };
+  QuantizeGroup<T, DST_DTYPE>(smem_group, group_output, group_size, lane_id,
+                              threads_per_group, y_s, min_8bit, max_8bit);
+}
 
-  vllm::vectorize_with_alignment<vec_size>(
-      smem_group,         // in (shared)
-      group_output,       // out (global quant tensor)
-      group_size,         // elements
-      lane_id,            // tid
-      threads_per_group,  // stride
-      scalar_op_quant);   // scalar handler
+inline int GetGroupsPerBlock(int64_t num_groups) {
+  if (num_groups % 16 == 0) {
+    return 16;
+  }
+  if (num_groups % 8 == 0) {
+    return 8;
+  }
+  if (num_groups % 4 == 0) {
+    return 4;
+  }
+  if (num_groups % 2 == 0) {
+    return 2;
+  }
+  return 1;
 }
 
 void per_token_group_quant_8bit(const torch::Tensor& input,
@@ -133,17 +171,7 @@ void per_token_group_quant_8bit(const torch::Tensor& input,
 
   constexpr int THREADS_PER_GROUP = 16;
 
-  int groups_per_block = 1;
-
-  if (num_groups % 16 == 0) {
-    groups_per_block = 16;
-  } else if (num_groups % 8 == 0) {
-    groups_per_block = 8;
-  } else if (num_groups % 4 == 0) {
-    groups_per_block = 4;
-  } else if (num_groups % 2 == 0) {
-    groups_per_block = 2;
-  }
+  const int groups_per_block = GetGroupsPerBlock(num_groups);
 
   auto dst_type = output_q.scalar_type();
   const int num_blocks = num_groups / groups_per_block;
@@ -225,8 +253,6 @@ __global__ void per_token_group_quant_8bit_packed_kernel(
 
   const int64_t block_group_offset = global_group_id * group_size;
 
-  float local_absmax = eps;
-
   const T* group_input = input + block_group_offset;
   DST_DTYPE* group_output =
       static_cast<DST_DTYPE*>(output_q) + block_group_offset;
@@ -235,29 +261,9 @@ __global__ void per_token_group_quant_8bit_packed_kernel(
   extern __shared__ __align__(16) char smem_raw[];
   T* smem = reinterpret_cast<T*>(smem_raw);
   T* smem_group = smem + local_group_id * group_size;
-
-  constexpr int vec_size = 16 / sizeof(T);
-  using vec_t = vllm::vec_n_t<T, vec_size>;
-
-  // copy global -> shared & compute absmax
-  auto scalar_op_cache = [&] __device__(T & dst, const T& src) {
-    float abs_v = fabsf(static_cast<float>(src));
-    local_absmax = fmaxf(local_absmax, abs_v);
-    dst = src;
-  };
-
-  vllm::vectorize_with_alignment<vec_size>(
-      group_input,        // in
-      smem_group,         // out (shared)
-      group_size,         // elements per group
-      lane_id,            // thread id
-      threads_per_group,  // stride in group
-      scalar_op_cache);   // scalar handler
-
-  local_absmax = GroupReduceMax(local_absmax);
-
-  float y_s = local_absmax / max_8bit;
-  y_s = exp2f(ceilf(log2f(fmaxf(fabsf(y_s), 1e-10f))));
+  const float y_s =
+      ComputeGroupScale<T, true>(group_input, smem_group, group_size, lane_id,
+                                 threads_per_group, eps, max_8bit);
 
   // pack 4 scales into a uint32
   if (lane_id == 0) {
@@ -284,19 +290,8 @@ __global__ void per_token_group_quant_8bit_packed_kernel(
 
   __syncthreads();
 
-  // quantize shared -> global 8-bit
-  auto scalar_op_quant = [&] __device__(DST_DTYPE & dst, const T& src) {
-    float q = fminf(fmaxf(static_cast<float>(src) / y_s, min_8bit), max_8bit);
-    dst = DST_DTYPE(q);
-  };
-
-  vllm::vectorize_with_alignment<vec_size>(
-      smem_group,         // in (shared)
-      group_output,       // out (global quant tensor)
-      group_size,         // elements
-      lane_id,            // tid
-      threads_per_group,  // stride
-      scalar_op_quant);   // scalar handler
+  QuantizeGroup<T, DST_DTYPE>(smem_group, group_output, group_size, lane_id,
+                              threads_per_group, y_s, min_8bit, max_8bit);
 }
 
 void per_token_group_quant_8bit_packed(const torch::Tensor& input,
@@ -337,17 +332,7 @@ void per_token_group_quant_8bit_packed(const torch::Tensor& input,
 
   constexpr int THREADS_PER_GROUP = 16;
 
-  int groups_per_block = 1;
-
-  if (num_groups % 16 == 0) {
-    groups_per_block = 16;
-  } else if (num_groups % 8 == 0) {
-    groups_per_block = 8;
-  } else if (num_groups % 4 == 0) {
-    groups_per_block = 4;
-  } else if (num_groups % 2 == 0) {
-    groups_per_block = 2;
-  }
+  const int groups_per_block = GetGroupsPerBlock(num_groups);
 
   auto dst_type = output_q.scalar_type();
   const int num_blocks = num_groups / groups_per_block;