quant_cuda_kernel.cu

#include <torch/all.h>
#include <cuda.h>
#include <cuda_runtime.h>
#include <cuda_fp16.h>

// half-tensor
#include <c10/cuda/CUDAStream.h>
#include <ATen/cuda/CUDATensorMethods.cuh>
#include <c10/cuda/CUDAGuard.h>

#define BLOCKWIDTH 128
#define BLOCKHEIGHT4 16

namespace vllm {
namespace squeezellm {

__device__ inline unsigned int as_unsigned(int i) {
  return *reinterpret_cast<unsigned int*>(&i);
}

// 4-bit matvec kernel (LUT-based)
__global__ void NUQ4MatMulKernel(
#ifndef USE_ROCM
    const half2* __restrict__ vec,
#else
    const __half2* __restrict__ vec,
#endif
    const int* __restrict__ mat,
#ifndef USE_ROCM
    half2* __restrict__ mul,
#else
    float2* __restrict__ mul,
#endif
    const __half* __restrict__ lookup_table, int height, int width, int batch,
    int vec_height) {

  const int blockwidth2 = BLOCKWIDTH / 2;

  int row = BLOCKHEIGHT4 * blockIdx.x;
  int col = BLOCKWIDTH * blockIdx.y + threadIdx.x;

#ifndef USE_ROCM
  __shared__ half2 blockvec[blockwidth2];
#else
  __shared__ __half2 blockvec[blockwidth2];
#endif

  __shared__ __half deq2[16][BLOCKWIDTH];
  int off = threadIdx.x;
  int column_offset = col * 16;
  for (int val = 0; val < 16; val += 1) {
    int lut_index = column_offset + val;
    deq2[val][off] = lookup_table[lut_index];
  }

  __half res;
#ifndef USE_ROCM
  half2 res2;
  half2 tmp2;
#else
  __half2 res2;
  __half2 tmp2;
#endif

  int i;
  int k;

  unsigned int tmp1;
  unsigned int lut_index1, lut_index2;

  for (int b = 0; b < batch; ++b) {
    i = width * row + col;
    res = __int2half_rd(0);
    k = 0;

    __syncthreads();
    if (threadIdx.x < blockwidth2)
      blockvec[threadIdx.x] =
          vec[b * vec_height / 2 + (row / BLOCKHEIGHT4) * blockwidth2 +
              threadIdx.x];
    __syncthreads();

    while (k < blockwidth2) {
      tmp1 = as_unsigned(mat[i]);

#ifndef USE_ROCM
      res2 = {};
      tmp2 = {};
#else
      res2.x = __half_as_ushort(__float2half(0));
      res2.y = __half_as_ushort(__float2half(0));
      tmp2.x = __half_as_ushort(__float2half(0));
      tmp2.y = __half_as_ushort(__float2half(0));
#endif

      lut_index1 = tmp1 & 0xF;
      lut_index2 = (tmp1 >> 4) & 0xF;
#ifndef USE_ROCM
      tmp2.x = deq2[lut_index1][off];
      tmp2.y = deq2[lut_index2][off];
#else
      tmp2.x = __half_as_ushort(deq2[lut_index1][off]);
      tmp2.y = __half_as_ushort(deq2[lut_index2][off]);
#endif
      res2 = __hfma2(tmp2, blockvec[k + 0], res2);

      lut_index1 = (tmp1 >> 8) & 0xF;
      lut_index2 = (tmp1 >> 12) & 0xF;
#ifndef USE_ROCM
      tmp2.x = deq2[lut_index1][off];
      tmp2.y = deq2[lut_index2][off];
#else
      tmp2.x = __half_as_ushort(deq2[lut_index1][off]);
      tmp2.y = __half_as_ushort(deq2[lut_index2][off]);
#endif
      res2 = __hfma2(tmp2, blockvec[k + 1], res2);

      lut_index1 = (tmp1 >> 16) & 0xF;
      lut_index2 = (tmp1 >> 20) & 0xF;
#ifndef USE_ROCM
      tmp2.x = deq2[lut_index1][off];
      tmp2.y = deq2[lut_index2][off];
#else
      tmp2.x = __half_as_ushort(deq2[lut_index1][off]);
      tmp2.y = __half_as_ushort(deq2[lut_index2][off]);
#endif
      res2 = __hfma2(tmp2, blockvec[k + 2], res2);

      lut_index1 = (tmp1 >> 24) & 0xF;
      lut_index2 = (tmp1 >> 28) & 0xF;
#ifndef USE_ROCM
      tmp2.x = deq2[lut_index1][off];
      tmp2.y = deq2[lut_index2][off];
#else
      tmp2.x = __half_as_ushort(deq2[lut_index1][off]);
      tmp2.y = __half_as_ushort(deq2[lut_index2][off]);
#endif
      res2 = __hfma2(tmp2, blockvec[k + 3], res2);

#ifndef USE_ROCM
      res = __hadd(__hadd(res2.x, res2.y), res);
#else
      res = __hadd(__hadd(__ushort_as_half(res2.x), __ushort_as_half(res2.y)),
                   res);
#endif

      i += width;
      k += 4;
    }

    // col%2 -> only set one of the two values
#ifndef USE_ROCM
    half2 res3 = {};
    if (col % 2 == 0) {
      res3.x = res;
    } else {
      res3.y = res;
    }
#else
    __half2 res3;
    res3.x = __half_as_ushort(__float2half(0));
    res3.y = __half_as_ushort(__float2half(0));
    if (col % 2 == 0) {
      res3.x = __half_as_ushort(res);
    } else {
      res3.y = __half_as_ushort(res);
    }
#endif

#ifndef USE_ROCM
    atomicAdd(&mul[b * width / 2 + col / 2], res3);
#else
    int tmp_addr = b * width / 2 + col / 2;
    atomicAdd(&(mul[tmp_addr].x), __half2float(__ushort_as_half(res3.x)));
    atomicAdd(&(mul[tmp_addr].y), __half2float(__ushort_as_half(res3.y)));
#endif
  }
}

}  // namespace squeezellm
}  // namespace vllm

// 4-bit matvec kernel (LUT-based)
void squeezellm_gemm(torch::Tensor vec, torch::Tensor mat, torch::Tensor mul,
                     torch::Tensor lookup_table) {
  int height = mat.size(0);
  int width = mat.size(1);

  int batch = vec.size(0);
  int vec_height = vec.size(1);

  dim3 blocks((height + BLOCKHEIGHT4 - 1) / BLOCKHEIGHT4,
              (width + BLOCKWIDTH - 1) / BLOCKWIDTH);
  dim3 threads(BLOCKWIDTH);

  const at::cuda::OptionalCUDAGuard device_guard(device_of(vec));
  const cudaStream_t stream = at::cuda::getCurrentCUDAStream();
  vllm::squeezellm::NUQ4MatMulKernel<<<blocks, threads, 0, stream>>>(
#ifndef USE_ROCM
      (half2*)vec.data<at::Half>(),
#else
      (__half2*)vec.data_ptr<at::Half>(),
#endif
      mat.data_ptr<int>(),
#ifndef USE_ROCM
      (half2*)mul.data<at::Half>(), (__half*)lookup_table.data<at::Half>(),
#else
      (float2*)mul.data_ptr<float>(),
      (__half*)lookup_table.data_ptr<at::Half>(),
#endif
      height, width, batch, vec_height);
}

#undef BLOCKWIDTH
#undef BLOCKHEIGHT4