revert pr 3628 to pass test_mla ci (#4219)

sgl-kernel/src/sgl-kernel/csrc/gemm/per_token_group_quant_fp8.cu

@@ -2,18 +2,17 @@
 #include <c10/util/Float8_e4m3fn.h>
 
 #include <cmath>
-#include <flashinfer/vec_dtypes.cuh>
 
 #include "utils.h"
 
 using FP8_TYPE = c10::Float8_e4m3fn;
 
-__device__ __forceinline__ float GroupReduce(float val, const int tid) {
-  val = fmaxf(val, __shfl_xor_sync(0xffff, val, 8));
-  val = fmaxf(val, __shfl_xor_sync(0xffff, val, 4));
-  val = fmaxf(val, __shfl_xor_sync(0xffff, val, 2));
-  val = fmaxf(val, __shfl_xor_sync(0xffff, val, 1));
-  return val;
+__device__ __forceinline__ float GroupReduceMax(volatile float* smem, const int tid) {
+  smem[tid] = fmaxf(smem[tid], smem[tid + 8]);
+  if (tid < 4) smem[tid] = fmaxf(smem[tid], smem[tid + 4]);
+  if (tid < 2) smem[tid] = fmaxf(smem[tid], smem[tid + 2]);
+  if (tid < 1) smem[tid] = fmaxf(smem[tid], smem[tid + 1]);
+  return smem[0];
 }
 
 template <typename T>
@@ -27,60 +26,45 @@ __global__ void per_token_group_quant_fp8_kernel(
     const float fp8_min,
     const float fp8_max) {
   const int groups_per_block = 16;
-  const int local_group_id = threadIdx.x / 16;
-  const int lane_id = threadIdx.x % 16;
-
   const int block_group_id = blockIdx.x * groups_per_block;
-  const int block_group_offset = (block_group_id + local_group_id) * group_size;
+  const int tid = threadIdx.x;
+  const int local_group_id = tid / 16;
+  const int local_tid = tid % 16;
 
-  __shared__ float s_absmax[16];
+  __shared__ float s_absmax[16][17];
 
   float local_absmax = eps;
 
-  const T* group_input = input + block_group_offset;
-  FP8_TYPE* group_output = static_cast<FP8_TYPE*>(output_q) + block_group_offset;
+  if (block_group_id + local_group_id < num_groups) {
+    const T* group_input = input + (block_group_id + local_group_id) * group_size;
+    FP8_TYPE* group_output = static_cast<FP8_TYPE*>(output_q) + (block_group_id + local_group_id) * group_size;
     float* scale_output = output_s + block_group_id + local_group_id;
 
-  constexpr uint32_t vec_size = 16 / sizeof(T);
-  using vec_t = flashinfer::vec_t<T, vec_size>;
-
-  const int32_t num_vec_elems = group_size / vec_size;
-
-  for (int32_t i = lane_id; i < num_vec_elems; i += 16) {
-    vec_t input_vec;
-    input_vec.cast_load(group_input + i * vec_size);
-
-#pragma unroll
-    for (uint32_t j = 0; j < vec_size; ++j) {
-      float val = static_cast<float>(input_vec[j]);
+    for (int i = local_tid; i < group_size; i += 16) {
+      float val = static_cast<float>(group_input[i]);
       float abs_val = fabsf(val);
       local_absmax = fmaxf(local_absmax, abs_val);
     }
-  }
 
-  local_absmax = GroupReduce(local_absmax, lane_id);
+    s_absmax[local_group_id][local_tid] = local_absmax;
+    __syncthreads();
 
-  if (lane_id == 0) {
-    s_absmax[local_group_id] = local_absmax;
+    if (local_tid < 8) {
+      GroupReduceMax(&s_absmax[local_group_id][0], local_tid);
     }
     __syncthreads();
 
-  const float group_absmax = s_absmax[local_group_id];
+    const float group_absmax = s_absmax[local_group_id][0];
     const float y_s = group_absmax / fp8_max;
 
-  if (lane_id == 0) {
+    if (local_tid == 0) {
       *scale_output = y_s;
     }
 
-  for (int32_t i = lane_id; i < num_vec_elems; i += 16) {
-    vec_t input_vec;
-    input_vec.cast_load(group_input + i * vec_size);
-
-#pragma unroll
-    for (uint32_t j = 0; j < vec_size; ++j) {
-      float val = static_cast<float>(input_vec[j]);
+    for (int i = local_tid; i < group_size; i += 16) {
+      float val = static_cast<float>(group_input[i]);
       float q_val = fminf(fmaxf(val / y_s, fp8_min), fp8_max);
-      group_output[i * vec_size + j] = FP8_TYPE(q_val);
+      group_output[i] = FP8_TYPE(q_val);
     }
   }
 }