MPI Intro and Practice

Intro

Definition

wiki:

• Message Passing Interface (MPI) is a standardized and portable message-passing standard
• designed by a group of researchers from academia and industry to function on a wide variety of parallel computing architectures.

Feature

• an interface, not a programming language
• Main model of HPC
• a cross-language communication protocol

Functions

• Communication
  • Point-to-point communication
    • Send
    • Recv
  • Collective communication
    • Broadcast, scatter/ gather, all to all, reduce, scan, barrier
• Almost all parallel programs can be described using the message passing model.

Concept

• Communicator:
  • Def: Communicator objects connect groups of processes in the MPI session.
  • Each communicator gives each contained process an independent identifier(id, called rank) and arranges its contained processes in an ordered topology.

Set up in Ubuntu 20.04

在这个阶段，简单地通过网络的教程进行 library or software 的安装是不现实的，还是得从根本上学会去解决问题，去看源文档(doc)的说明。

I. Download

• Download mpich-3.4.1.tar.gz at https://www.mpich.org/downloads/
• 版本会更新，地址应该不会变

II. 解压后进入目录

tar -xzvf mpich-3.4.1.tar.gz
cd mpich-3.4.1

III. 配置

./configure --prefix=/home/Desktop/HPC/mpich-3.4.1/mpich-install 2>&1 | tee c.txt

• 这个地方根据自己的安装路径，我就配置在当前的/home/Desktop/HPC/mpich-3.4.1文件夹下

• 然后出现两个坑

  • error: no ch4 netmod selected
  • 
  • 根据提示加上 --with-device=ch4:ofi 即可
  • 加上后再次报错No Fortran compiler found. If you don't need to build any Fortran programs, you can disable Fortran support using --disable-fortran. If you do want to build Fortran programs, you need to install a Fortran compiler such as gfortran or ifort before you can proceed.
  • 这是因为没有安装Fortran compiler
  • 根据提示加上 --disable-fortran 即可

./configure --disable-fortran  --with-device=ch4:ofi  --prefix=/home/Desktop/HPC/mpich-3.4.1/mpich-install 2>&1 | tee c.txt

• 成功配置

  

接下来 ->

make    		#等待一段漫长的时间
make install    #权限不够加 sudo

IV. 添加环境变量

sudo gedit ~/.bashrc

• 打开.bashrc 文件后在末尾添加

export MPI_ROOT=/home/Desktop/HPC/mpich-3.4.1/mpich-install #这一步对应你自己的安装地址
export PATH=$MPI_ROOT/bin:$PATH
export MANPATH=$MPI_ROOT/man:$MANPATH

• 然后激活

source ~/.bashrc

• which mpicc 查看位置信息
• mpichversion 查看版本信息，出现版本号说明安装成功

.

运行程序

I. 创建文件hello.c

#include "mpi.h"
#include <stdio.h>

int main( int argc, char *argv[] )
{
    int rank, size;
    MPI_Init( &argc, &argv );
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    MPI_Comm_size( MPI_COMM_WORLD, &size );
    printf( "I am %d of %d\n", rank, size );
    MPI_Finalize();
    return 0;
}

II. 编译

mpicc hellow.c -o hellow

III. 运行

mpirun -n 2 ./hellow

.