Hybrid Multithreaded/OpenMP + MPI parallel Programs

混合编程需要注意的问题

https://www.nhr.kit.edu/userdocs/horeka/batch_slurm_mpi_multithread/ 看这个

还有个ppt 16

google hydrid openmpi openmp

intelmpi 编译

这里值得要注意的是，似乎直接用mpif90/mpicxx编译的库会报错，所以需要用

icc -openmp hello.cpp -o hello -DMPICH_IGNORE_CXX_SEEK -L/Path/to/mpi/lib/ -lmpi_mt -lmpiic -I/path/to/mpi/include
其中-DMPICH_IGNORE_CXX_SEEK为防止MPI2协议中一个重复定义问题所使用的选项，为了保证线程安全，必须使用mpi_mt库

对于intel的mpirun，必须在mpirun后加上-env I_MPI_PIN_DOMAIN omp使得每个mpi进程会启动openmp线程。

通过export OMP_NUM_THREADS来控制每个MPI产生多少线程。

OpenMPI 如何实现mult-thread(OpenMP)²

检查编译安装支持mult-thread

shell$ ompi_info | grep "Thread support"
          Thread support: posix (MPI_THREAD_MULTIPLE: yes, OPAL support: yes, OMPI progress: no, Event lib: yes)
shell$

“MPI_THREAD_MULTIPLE: yes”说明是支持的。

在C程序里支持mult-thread

#include <mpi.h>
int MPI_Init_thread(int *argc, char ***argv,
    int required, int *provided)

argc
        C/C++ only: Pointer to the number of arguments.
argv
        C/C++ only: Argument vector.
required
        Desired level of thread support (integer).
provided
        Available level of thread support (integer).

required 可选值 分别是0，1，2，3

MPI_THREAD_SINGLE
        Only one thread will execute.
MPI_THREAD_FUNNELED
        If the process is multithreaded, only the thread that called MPI_Init_thread will make MPI calls.
MPI_THREAD_SERIALIZED
        If the process is multithreaded, only one thread will make MPI library calls at one time.
MPI_THREAD_MULTIPLE
        If the process is multithreaded, multiple threads may call MPI at once with no restrictions.

MPI_Init_thread调用MPI_thread_SINGLE等同于调用MPI_Init。

注意

3.1.6的多线程支持还在初级阶段。开销很高（虽然我不知道为什么）

需要进一步的研究学习

学习MapReduce或者Hadoop？ pthread vs openmp?

遇到的问题

暂无

开题缘由、总结、反思、吐槽~~

参考文献

https://blog.csdn.net/Morizen/article/details/113863591

[2] OpenMPI-multThread