我是使用GPU进行并行编程的新手，所以如果问题广泛或模糊，我会道歉。我知道CULA库中有一些并行的SVD功能，但是如果我有大量相对较小的矩阵来分解，应该采取什么策略呢？例如，我有n矩阵d，n很大且d很小。如何并行化这个过程？谁能给我一个提示？
答案 0 :(得分：7)
我之前的回答已经过时了。截至2015年2月，CUDA 7（目前处于候选版本）在其cuSOLVER库中提供完整的SVD功能。下面，我将提供一个使用CUDA cuSOLVER生成奇异值分解的示例。
关于您正在上升的具体问题（计算几个小尺寸矩阵的SVD ），您应该使用流来调整我在下面提供的示例。要将流关联到每个任务，您可以使用
cudaStreamCreate()
和
cusolverDnSetStream()
<强> kernel.cu
#include "cuda_runtime.h"
#include "device_launch_parameters.h"
#include<iostream>
#include<iomanip>
#include<stdlib.h>
#include<stdio.h>
#include<assert.h>
#include<math.h>
#include <cusolverDn.h>
#include <cuda_runtime_api.h>
#include "Utilities.cuh"
/********/
/* MAIN */
/********/
int main(){
// --- gesvd only supports Nrows >= Ncols
// --- column major memory ordering
const int Nrows = 7;
const int Ncols = 5;
// --- cuSOLVE input/output parameters/arrays
int work_size = 0;
int *devInfo; gpuErrchk(cudaMalloc(&devInfo, sizeof(int)));
// --- CUDA solver initialization
cusolverDnHandle_t solver_handle;
cusolverDnCreate(&solver_handle);
// --- Setting the host, Nrows x Ncols matrix
double *h_A = (double *)malloc(Nrows * Ncols * sizeof(double));
for(int j = 0; j < Nrows; j++)
for(int i = 0; i < Ncols; i++)
h_A[j + i*Nrows] = (i + j*j) * sqrt((double)(i + j));
// --- Setting the device matrix and moving the host matrix to the device
double *d_A; gpuErrchk(cudaMalloc(&d_A, Nrows * Ncols * sizeof(double)));
gpuErrchk(cudaMemcpy(d_A, h_A, Nrows * Ncols * sizeof(double), cudaMemcpyHostToDevice));
// --- host side SVD results space
double *h_U = (double *)malloc(Nrows * Nrows * sizeof(double));
double *h_V = (double *)malloc(Ncols * Ncols * sizeof(double));
double *h_S = (double *)malloc(min(Nrows, Ncols) * sizeof(double));
// --- device side SVD workspace and matrices
double *d_U; gpuErrchk(cudaMalloc(&d_U, Nrows * Nrows * sizeof(double)));
double *d_V; gpuErrchk(cudaMalloc(&d_V, Ncols * Ncols * sizeof(double)));
double *d_S; gpuErrchk(cudaMalloc(&d_S, min(Nrows, Ncols) * sizeof(double)));
// --- CUDA SVD initialization
cusolveSafeCall(cusolverDnDgesvd_bufferSize(solver_handle, Nrows, Ncols, &work_size));
double *work; gpuErrchk(cudaMalloc(&work, work_size * sizeof(double)));
// --- CUDA SVD execution
cusolveSafeCall(cusolverDnDgesvd(solver_handle, 'A', 'A', Nrows, Ncols, d_A, Nrows, d_S, d_U, Nrows, d_V, Ncols, work, work_size, NULL, devInfo));
int devInfo_h = 0; gpuErrchk(cudaMemcpy(&devInfo_h, devInfo, sizeof(int), cudaMemcpyDeviceToHost));
if (devInfo_h != 0) std::cout << "Unsuccessful SVD execution\n\n";
// --- Moving the results from device to host
gpuErrchk(cudaMemcpy(h_S, d_S, min(Nrows, Ncols) * sizeof(double), cudaMemcpyDeviceToHost));
gpuErrchk(cudaMemcpy(h_U, d_U, Nrows * Nrows * sizeof(double), cudaMemcpyDeviceToHost));
gpuErrchk(cudaMemcpy(h_V, d_V, Ncols * Ncols * sizeof(double), cudaMemcpyDeviceToHost));
std::cout << "Singular values\n";
for(int i = 0; i < min(Nrows, Ncols); i++)
std::cout << "d_S["<<i<<"] = " << std::setprecision(15) << h_S[i] << std::endl;
std::cout << "\nLeft singular vectors - For y = A * x, the columns of U span the space of y\n";
for(int j = 0; j < Nrows; j++) {
printf("\n");
for(int i = 0; i < Nrows; i++)
printf("U[%i,%i]=%f\n",i,j,h_U[j*Nrows + i]);
}
std::cout << "\nRight singular vectors - For y = A * x, the columns of V span the space of x\n";
for(int i = 0; i < Ncols; i++) {
printf("\n");
for(int j = 0; j < Ncols; j++)
printf("V[%i,%i]=%f\n",i,j,h_V[j*Ncols + i]);
}
cusolverDnDestroy(solver_handle);
return 0;
}
<强> Utilities.cuh
#ifndef UTILITIES_CUH
#define UTILITIES_CUH
extern "C" int iDivUp(int, int);
extern "C" void gpuErrchk(cudaError_t);
extern "C" void cusolveSafeCall(cusolverStatus_t);
#endif
<强> Utilities.cu
#include <stdio.h>
#include <assert.h>
#include "cuda_runtime.h"
#include <cuda.h>
#include <cusolverDn.h>
/*******************/
/* iDivUp FUNCTION */
/*******************/
extern "C" int iDivUp(int a, int b){ return ((a % b) != 0) ? (a / b + 1) : (a / b); }
/********************/
/* CUDA ERROR CHECK */
/********************/
// --- Credit to http://stackoverflow.com/questions/14038589/what-is-the-canonical-way-to-check-for-errors-using-the-cuda-runtime-api
void gpuAssert(cudaError_t code, char *file, int line, bool abort=true)
{
if (code != cudaSuccess)
{
fprintf(stderr,"GPUassert: %s %s %d\n", cudaGetErrorString(code), file, line);
if (abort) { exit(code); }
}
}
extern "C" void gpuErrchk(cudaError_t ans) { gpuAssert((ans), __FILE__, __LINE__); }
/**************************/
/* CUSOLVE ERROR CHECKING */
/**************************/
static const char *_cudaGetErrorEnum(cusolverStatus_t error)
{
switch (error)
{
case CUSOLVER_STATUS_SUCCESS:
return "CUSOLVER_SUCCESS";
case CUSOLVER_STATUS_NOT_INITIALIZED:
return "CUSOLVER_STATUS_NOT_INITIALIZED";
case CUSOLVER_STATUS_ALLOC_FAILED:
return "CUSOLVER_STATUS_ALLOC_FAILED";
case CUSOLVER_STATUS_INVALID_VALUE:
return "CUSOLVER_STATUS_INVALID_VALUE";
case CUSOLVER_STATUS_ARCH_MISMATCH:
return "CUSOLVER_STATUS_ARCH_MISMATCH";
case CUSOLVER_STATUS_EXECUTION_FAILED:
return "CUSOLVER_STATUS_EXECUTION_FAILED";
case CUSOLVER_STATUS_INTERNAL_ERROR:
return "CUSOLVER_STATUS_INTERNAL_ERROR";
case CUSOLVER_STATUS_MATRIX_TYPE_NOT_SUPPORTED:
return "CUSOLVER_STATUS_MATRIX_TYPE_NOT_SUPPORTED";
}
return "<unknown>";
}
inline void __cusolveSafeCall(cusolverStatus_t err, const char *file, const int line)
{
if(CUSOLVER_STATUS_SUCCESS != err) {
fprintf(stderr, "CUSOLVE error in file '%s', line %d\n %s\nerror %d: %s\nterminating!\n",__FILE__, __LINE__,err, \
_cudaGetErrorEnum(err)); \
cudaDeviceReset(); assert(0); \
}
}
extern "C" void cusolveSafeCall(cusolverStatus_t err) { __cusolveSafeCall(err, __FILE__, __LINE__); }
答案 1 :(得分：4)
您可以查看CULA博客的Batched Operations帖子，了解您的问题。
修改
根据我从下面的评论中理解，您希望每个线程计算一个单独的SVD。因此，基本上每个线程都应该执行标准的顺序SVD方案。对于一些可能有用的参考：
Golub, Van Loan, Matrix Computations
但是，如果您使用这种方法，我担心您将无法再使用cuBLAS，因为那些host函数无法从device调用（除非您没有计算能力>3.5，请参阅simpleDevLibCUBLAS示例。）。但基本上这样我认为你是以某种方式自己实现批量概念。
如果您决定采用更标准的并行GPU实现，下面的参考可能会引起关注：
答案 2 :(得分：0)
以上答案现已过期。从CUDA 9.0开始，cuSOLVER库已经基于Jacobi方法进行了批量SVD计算。下面是一个完整的示例：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <cuda_runtime.h>
#include <cusolverDn.h>
#include "Utilities.cuh"
#include "TimingGPU.cuh"
//#define FULLSVD
//#define PRINTRESULTS
/********/
/* MAIN */
/********/
int main() {
const int M = 3;
const int N = 3;
const int lda = M;
//const int numMatrices = 3;
const int numMatrices = 16384;
TimingGPU timerGPU;
// --- Setting the host matrix
double *h_A = (double *)malloc(lda * N * numMatrices * sizeof(double));
for (unsigned int k = 0; k < numMatrices; k++)
for (unsigned int i = 0; i < M; i++){
for (unsigned int j = 0; j < N; j++){
h_A[k * M * N + j * M + i] = (1. / (k + 1)) * (i + j * j) * (i + j);
//printf("%d %d %f\n", i, j, h_A[j*M + i]);
}
}
// --- Setting the device matrix and moving the host matrix to the device
double *d_A; gpuErrchk(cudaMalloc(&d_A, M * N * numMatrices * sizeof(double)));
gpuErrchk(cudaMemcpy(d_A, h_A, M * N * numMatrices * sizeof(double), cudaMemcpyHostToDevice));
// --- host side SVD results space
double *h_S = (double *)malloc(N * numMatrices * sizeof(double));
double *h_U = NULL;
double *h_V = NULL;
#ifdef FULLSVD
h_U = (double *)malloc(M * M * numMatrices * sizeof(double));
h_V = (double *)malloc(N * N * numMatrices * sizeof(double));
#endif
// --- device side SVD workspace and matrices
int work_size = 0;
int *devInfo; gpuErrchk(cudaMalloc(&devInfo, sizeof(int)));
double *d_S; gpuErrchk(cudaMalloc(&d_S, N * numMatrices * sizeof(double)));
double *d_U = NULL;
double *d_V = NULL;
#ifdef FULLSVD
gpuErrchk(cudaMalloc(&d_U, M * M * numMatrices * sizeof(double)));
gpuErrchk(cudaMalloc(&d_V, N * N * numMatrices * sizeof(double)));
#endif
double *d_work = NULL; /* devie workspace for gesvdj */
int devInfo_h = 0; /* host copy of error devInfo_h */
// --- Parameters configuration of Jacobi-based SVD
const double tol = 1.e-7;
const int maxSweeps = 15;
cusolverEigMode_t jobz; // --- CUSOLVER_EIG_MODE_VECTOR - Compute eigenvectors; CUSOLVER_EIG_MODE_NOVECTOR - Compute singular values only
#ifdef FULLSVD
jobz = CUSOLVER_EIG_MODE_VECTOR;
#else
jobz = CUSOLVER_EIG_MODE_NOVECTOR;
#endif
const int econ = 0; // --- econ = 1 for economy size
// --- Numerical result parameters of gesvdj
double residual = 0;
int executedSweeps = 0;
// --- CUDA solver initialization
cusolverDnHandle_t solver_handle = NULL;
cusolveSafeCall(cusolverDnCreate(&solver_handle));
// --- Configuration of gesvdj
gesvdjInfo_t gesvdj_params = NULL;
cusolveSafeCall(cusolverDnCreateGesvdjInfo(&gesvdj_params));
// --- Set the computation tolerance, since the default tolerance is machine precision
cusolveSafeCall(cusolverDnXgesvdjSetTolerance(gesvdj_params, tol));
// --- Set the maximum number of sweeps, since the default value of max. sweeps is 100
cusolveSafeCall(cusolverDnXgesvdjSetMaxSweeps(gesvdj_params, maxSweeps));
// --- Query the SVD workspace
cusolveSafeCall(cusolverDnDgesvdjBatched_bufferSize(
solver_handle,
jobz, // --- Compute the singular vectors or not
M, // --- Nubmer of rows of A, 0 <= M
N, // --- Number of columns of A, 0 <= N
d_A, // --- M x N
lda, // --- Leading dimension of A
d_S, // --- Square matrix of size min(M, N) x min(M, N)
d_U, // --- M x M if econ = 0, M x min(M, N) if econ = 1
lda, // --- Leading dimension of U, ldu >= max(1, M)
d_V, // --- N x N if econ = 0, N x min(M,N) if econ = 1
lda, // --- Leading dimension of V, ldv >= max(1, N)
&work_size,
gesvdj_params,
numMatrices));
gpuErrchk(cudaMalloc(&d_work, sizeof(double) * work_size));
// --- Compute SVD
timerGPU.StartCounter();
cusolveSafeCall(cusolverDnDgesvdjBatched(
solver_handle,
jobz, // --- Compute the singular vectors or not
M, // --- Number of rows of A, 0 <= M
N, // --- Number of columns of A, 0 <= N
d_A, // --- M x N
lda, // --- Leading dimension of A
d_S, // --- Square matrix of size min(M, N) x min(M, N)
d_U, // --- M x M if econ = 0, M x min(M, N) if econ = 1
lda, // --- Leading dimension of U, ldu >= max(1, M)
d_V, // --- N x N if econ = 0, N x min(M, N) if econ = 1
lda, // --- Leading dimension of V, ldv >= max(1, N)
d_work,
work_size,
devInfo,
gesvdj_params,
numMatrices));
printf("Calculation of the singular values only: %f ms\n\n", timerGPU.GetCounter());
gpuErrchk(cudaMemcpy(&devInfo_h, devInfo, sizeof(int), cudaMemcpyDeviceToHost));
gpuErrchk(cudaMemcpy(h_S, d_S, sizeof(double) * N * numMatrices, cudaMemcpyDeviceToHost));
#ifdef FULLSVD
gpuErrchk(cudaMemcpy(h_U, d_U, sizeof(double) * lda * M * numMatrices, cudaMemcpyDeviceToHost));
gpuErrchk(cudaMemcpy(h_V, d_V, sizeof(double) * lda * N * numMatrices, cudaMemcpyDeviceToHost));
#endif
#ifdef PRINTRESULTS
printf("SINGULAR VALUES \n");
printf("_______________ \n");
for (int k = 0; k < numMatrices; k++) {
for (int p = 0; p < N; p++)
printf("Matrix nr. %d; SV nr. %d; Value = %f\n", k, p, h_S[k * N + p]);
printf("\n");
}
#ifdef FULLSVD
printf("SINGULAR VECTORS U \n");
printf("__________________ \n");
for (int k = 0; k < numMatrices; k++) {
for (int q = 0; q < (1 - econ) * M + econ * min(M, N); q++)
for (int p = 0; p < M; p++)
printf("Matrix nr. %d; U nr. %d; Value = %f\n", k, p, h_U[((1 - econ) * M + econ * min(M, N)) * M * k + q * M + p]);
printf("\n");
}
printf("SINGULAR VECTORS V \n");
printf("__________________ \n");
for (int k = 0; k < numMatrices; k++) {
for (int q = 0; q < (1 - econ) * N + econ * min(M, N); q++)
for (int p = 0; p < N; p++)
printf("Matrix nr. %d; V nr. %d; Value = %f\n", k, p, h_V[((1 - econ) * N + econ * min(M, N)) * N * k + q * N + p]);
printf("\n");
}
#endif
#endif
if (0 == devInfo_h){
printf("gesvdj converges \n");
}
else if (0 > devInfo_h){
printf("%d-th parameter is wrong \n", -devInfo_h);
exit(1);
}
else{
printf("WARNING: devInfo_h = %d : gesvdj does not converge \n", devInfo_h);
}
// --- Free resources
if (d_A) gpuErrchk(cudaFree(d_A));
if (d_S) gpuErrchk(cudaFree(d_S));
#ifdef FULLSVD
if (d_U) gpuErrchk(cudaFree(d_U));
if (d_V) gpuErrchk(cudaFree(d_V));
#endif
if (devInfo) gpuErrchk(cudaFree(devInfo));
if (d_work) gpuErrchk(cudaFree(d_work));
if (solver_handle) cusolveSafeCall(cusolverDnDestroy(solver_handle));
if (gesvdj_params) cusolveSafeCall(cusolverDnDestroyGesvdjInfo(gesvdj_params));
gpuErrchk(cudaDeviceReset());
return 0;
}