I tried matrix multiplication using cublasGemmEx. A and b are 1X1 half matrix. The result is always zero if i set the compute type and output date type to CUDA_R_16F. And the result is correct if i set compute type and output date type to CUDA_R_32F.
My cuda version is 10.2, gpu is T4. I build my code with command ‘nvcc -arch=sm_75 test_cublas.cu -o test_cublas -lcublas’
Is there anything wrong?
#include "cublas_v2.h"
#include "library_types.h"
#include <stdio.h>
__global__ void init_kernel(half *a, half *b, half *c_half, float *c_float)
{
*a = __float2half_rn(1.0);
*b = __float2half_rn(1.5);
*c_half = __float2half_rn(0.0);
*c_float = 0.0;
}
__global__ void print_gpu_values(half *a, half *b, half *c_half, float *c_float)
{
printf("a %f, b %f, c_half %f, c_float %f\n", __half2float(*a), __half2float(*b), __half2float(*c_half), *c_float);
}
int main(int argc, char **argv)
{
cudaStream_t cudaStream;
if (cudaSuccess != cudaStreamCreateWithFlags(&cudaStream, cudaStreamNonBlocking))
{
printf("create cuda stream failed\n");
exit(-1);
}
cublasHandle_t handle;
cublasCreate(&handle);
if (CUBLAS_STATUS_SUCCESS != cublasSetStream(handle, cudaStream))
{
printf("cublas set stream failed\n");
exit(-1);
}
half *a;
half *b;
half *c_half;
float *c_float;
cudaMalloc(&a, sizeof(half));
cudaMalloc(&b, sizeof(half));
cudaMalloc(&c_half, sizeof(half));
cudaMalloc(&c_float,sizeof(float));
float alpha = 1.0;
float beta = 1.0;
init_kernel<<<1, 1, 0, cudaStream>>>(a, b, c_half, c_float);
if (CUBLAS_STATUS_SUCCESS != cublasGemmEx(handle, CUBLAS_OP_N, CUBLAS_OP_N, 1, 1, 1,
&alpha, b, CUDA_R_16F, 1, a, CUDA_R_16F, 1, &beta, c_half, CUDA_R_16F, 1, CUDA_R_16F, CUBLAS_GEMM_DEFAULT_TENSOR_OP))
{
printf("cublasGemmEx failed\n");
exit(-1);
}
if (CUBLAS_STATUS_SUCCESS != cublasGemmEx(handle, CUBLAS_OP_N, CUBLAS_OP_N, 1, 1, 1,
&alpha, b, CUDA_R_16F, 1, a, CUDA_R_16F, 1, &beta, c_float, CUDA_R_32F, 1, CUDA_R_32F, CUBLAS_GEMM_DEFAULT_TENSOR_OP))
{
printf("cublasGemmEx failed\n");
exit(-1);
}
print_gpu_values<<<1, 1, 0, cudaStream>>>(a, b, c_half, c_float);
cudaStreamSynchronize(cudaStream);
return 0;
}
Thanks for your answers.