一个编写最快，运行很慢的 cuda gemm kernel, 占位 kernel

C = alpha*A*B + beta*C

每个线程负责一个C(i , j) 元素的计算。

1, gemm nn

__global__
void dgemm_NN( lint M,
                    lint N,
                    lint K,
                    double* Ad,
                    lint lda,
                    double* Bd,
                    lint ldb,
                    double* Cd,
                    lint ldc,
                    double alpha,
                    double beta )
{
    lint i = blockIdx.x * blockDim.x + threadIdx.x;
    lint j = blockIdx.y * blockDim.y + threadIdx.y;
    double sigma = 0.0;
    for(lint k=0; k<K; k++)
        sigma += Ad[i + k*lda]*Bd[k + j*ldb];

    Cd[i + j*ldc] = alpha*sigma + beta*Cd[i + j*ldc];
}

2, gemm nt

__global__
void dgemm_NT( int opA,
                    int opB,
                    lint M,
                    lint N,
                    lint K,
                    double* Ad,
                    lint lda,
                    double* Bd,
                    lint ldb,
                    double* Cd,
                    lint ldc,
                    double alpha,
                    double beta )
{
    lint i = blockIdx.x * blockDim.x + threadIdx.x;
    lint j = blockIdx.y * blockDim.y + threadIdx.y;
    double sigma = 0.0;
    if(i<M && j<N){
        for(lint k=0; k<K; k++)
            sigma += Ad[i + k*lda]*Bd[k*ldb + j];

        Cd[i + j*ldc] = alpha*sigma + beta*Cd[i + j*ldc];
    }
}