"hello world" 使用OpenMP和MPI混合的C程序

Question

我正在尝试获得一个同时使用OpenMP和MPI工作的"hello world"程序。我从这里的例子开始

http://www.slac.stanford.edu/comp/unix/farm/mpi_and_openmp.html

但我无法重现输出。这是我使用的确切来源：

#include <stdio.h>
#include <mpi.h>
#include <omp.h>
int main(int argc, char *argv[]) {
  int numprocs, rank, namelen;
  char processor_name[MPI_MAX_PROCESSOR_NAME];
  int iam = 0, np = 1;
  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Get_processor_name(processor_name, &namelen);
  //omp_set_num_threads(4);
#pragma omp parallel default(shared) private(iam, np)
  {
    np = omp_get_num_threads();
    iam = omp_get_thread_num();
    printf("Hello from thread %d out of %d from process %d out of %d on %sn",
           iam, np, rank, numprocs, processor_name);
  }
  MPI_Finalize();
}

我使用的是运行 Ubuntu 12.10 的双处理器至强工作站（2x6 内核）。我可以轻松让使用 MPI 或 OpenMP（但不能同时使用两者）的程序工作。

我使用命令编译了上面的源代码

mpicc -fopenmp hello.c -o hello

然后使用

export OMP_NUM_THREADS=4
mpirun ./hello -np 2 -x OMP_NUM_THREADS

这是我得到的输出：

Hello from thread 0 out of 4 from process 0 out of 1 on SteinbergT5600Linux
Hello from thread 2 out of 4 from process 0 out of 1 on SteinbergT5600Linux
Hello from thread 1 out of 4 from process 0 out of 1 on SteinbergT5600Linux
Hello from thread 3 out of 4 from process 0 out of 1 on SteinbergT5600Linux

根据示例，我应该得到这样的东西：

Hello from thread 0 out of 4 from process 0 out of 2 on SteinbergT5600Linux
Hello from thread 2 out of 4 from process 0 out of 2 on SteinbergT5600Linux
Hello from thread 1 out of 4 from process 0 out of 2 on SteinbergT5600Linux
Hello from thread 3 out of 4 from process 0 out of 2 on SteinbergT5600Linux
Hello from thread 0 out of 4 from process 1 out of 2 on SteinbergT5600Linux
Hello from thread 2 out of 4 from process 1 out of 2 on SteinbergT5600Linux
Hello from thread 1 out of 4 from process 1 out of 2 on SteinbergT5600Linux
Hello from thread 3 out of 4 from process 1 out of 2 on SteinbergT5600Linux

谁能给我一个提示，说明我做错了什么？据我所知，我完全复制了上面链接中的示例。

Answer 1

您将程序名称指定为要mpirun的第一个参数，因此其余参数将被忽略（值得注意的是：-np 2）。因此，对于-np，您可以获得系统范围的默认值。

改变：

mpirun ./hello -np 2 -x OMP_NUM_THREADS

到：

mpirun -np 2 -x OMP_NUM_THREADS ./hello

---

旁注：我在我的机器上对此进行了测试。此处-np的默认值为 3 。在您的计算机上，默认值似乎为1