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<div style="text-align: center;"><big style="font-weight: bold;"><big>實作八： MPICH 實作練習</big></big></div>
}}}
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[wiki:mpich 實作八 ('MPI完全解說'版本)] - [grid:raw-attachment:wiki:mpich:MPICH-1.3.ppt 課程投影片]

◢ <[wiki:YM_Course_2009/Lab7 實作七]> | <[wiki:YM_Course_2009 回課程大綱]> ▲ | <[wiki:YM_Course_2009/Lab9 實作九]> ◣

== MPI 環境設定 ==

 * 使用你的帳號登入: ym**
{{{
login as: ym24
ym24@bio.classcloud.org's password: ******
ym24@bio001:~$ ssh-keygen -t rsa
}}}
 * 產生 SSH 認證金鑰
{{{
Generating public/private rsa key pair.
Enter file in which to save the key (/home/ym24/.ssh/id_rsa):  <<< 請按 Enter
Created directory '/home/ym24/.ssh'.
Enter passphrase (empty for no passphrase):            <<< 請按 Enter
Enter same passphrase again:                     <<< 請按 Enter
Your identification has been saved in /home/ym24/.ssh/id_rsa.
Your public key has been saved in /home/ym24/.ssh/id_rsa.pub.
The key fingerprint is:
2a:6c:05:f8:24:38:db:79:b9:4f:0c:74:da:c5:16:05 ym24@bio001
}}}
 * 進行金鑰交換
{{{
ym24@bio001:~$ cp .ssh/id_rsa.pub .ssh/authorized_keys
}}}
 * 設定 MPD 設定檔跟 MPI 的執行檔路徑
{{{
ym24@bio001:~$ echo "MPD_SECRETWORD=${user}$$" > ~/.mpd.conf
ym24@bio001:~$ chmod 600 .mpd.conf
ym24@bio001:~$ for ((i=2;i<=12;i++)); do echo "192.168.129.$i" >> mpd.hosts; done
ym24@bio001:~$ export PATH=$PATH:/opt/mpich2/bin
ym24@bio001:~$ which mpdboot
/opt/mpich2/bin/mpdboot
}}}
 * 設定 dsh (distributed shell)[http://packages.debian.org/stable/net/dsh *], 我們可以使用 dsh 指令逐台執行.
{{{
ym24@bio001:~$ mkdir -p .dsh/
ym24@bio001:~$ cp mpd.hosts .dsh/machines.list
ym24@bio001:~$ dsh -a hostname
}}}
 * 用使用者的身分執行 mpd
{{{
ym24@bio001:~$ mpdboot -n 7
}}}
 * 用 mpdtrace 檢查 mpd 執行狀態
{{{
ym24@bio001:~$ mpdtrace 
bio002
bio006
bio012
bio011
bio005
bio004
bio003
bio010
bio009
bio008
bio007
}}}
 * 用 mpdringtest 做 mpd 訊息傳遞效能測試
{{{
ym24@bio002:~$ mpdringtest 1000
time for 1000 loops = 1.07995414734 seconds
}}}
 * 用 mpiexec 執行 cpi 範例程式
{{{
ym24@bio001:~$ mpiexec -n 3 /opt/mpich2/share/mpich2/examples/cpi
Process 0 of 1 is on bio001
pi is approximately 3.1415926544231341, Error is 0.0000000008333410
wall clock time = 0.000295
Process 0 of 1 is on bio001
pi is approximately 3.1415926544231341, Error is 0.0000000008333410
wall clock time = 0.000287
Process 0 of 1 is on bio001
pi is approximately 3.1415926544231341, Error is 0.0000000008333410
wall clock time = 0.000277
}}}

== 範例一：test1.c ==

[[PageOutline]]

 * 貼上 test1.c
{{{
ym24@bio001:~$ cat << EOF > test1.c
#include <stdio.h>
#include <mpi.h>
main (int argc, char **argv)
{
  int rank, size, len;
  char name[MPI_MAX_PROCESSOR_NAME];
  MPI_Init(&argc, &argv);
  int myid, numprocs;

  /* 取得 node 總數 */
  MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
  /* 取得本身 node id / rank */
  MPI_Comm_rank(MPI_COMM_WORLD,&myid);
  /* 取得本身 host name */
  MPI_Get_processor_name(name, &len);
  printf("This is machine %d of %d name = %s\n", myid, numprocs, name);

  MPI_Finalize();
}
EOF
}}}
 * 用 mpicc 編譯 test1.c
{{{
ym24@bio001:~$ mpicc -o test1 test1.c
}}}
 * 用 mpiexec 執行 test1 程式
{{{
ym24@bio001:~$ mpiexec -n 1 ./test1
This is machine 0 of 1 name = bio001
ym24@bio001:~$ mpiexec -n 12 ./test1
}}}

== 範例二：test2.c ==
[[PageOutline]]

 * here is test2.c
{{{
ym24@bio001:~$ cat << EOF > test2.c
#include <mpi.h>
#include <stdio.h>
main(int argc,char **argv) { 
  int n, myrank, numprocs;
  MPI_Status status;
  MPI_Init(&argc,&argv);
  MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
  MPI_Comm_rank(MPI_COMM_WORLD,&myrank);

  /* node 0 will send the first message */
  if(myrank == 0) {
    n = myrank;
    MPI_Send(&n, 1, MPI_INT, 1, 99, MPI_COMM_WORLD);
    printf("[Ndde %d]「%d」 >> [Node %d]\n\n", myrank, n, myrank+1);
  }

  /* node 1 to node n-2 will send message to the next node */
  if(myrank>0 && myrank<numprocs-1) {
    MPI_Recv(&n, 1, MPI_INT, myrank-1, 99, MPI_COMM_WORLD, &status);
    printf("[Node %d] << 「%d」[Node %d]\n", myrank, n, status.MPI_SOURCE);
    n = myrank; MPI_Send(&n, 1, MPI_INT, myrank+1, 99, MPI_COMM_WORLD);
    printf("[Ndde %d]「%d」 >> [Node %d]\n\n", myrank, n, myrank+1);
  }

 /* the final node n-1 will not send any message but receive*/
  if(myrank==numprocs-1) {
    MPI_Recv(&n, 1, MPI_INT, myrank-1, 99, MPI_COMM_WORLD, &status);
    printf("[Node %d] << 「%d」[Node %d]\n", myrank, n, status.MPI_SOURCE);
    }

  MPI_Finalize();
} 
EOF
}}}
 * 用 mpicc 編譯 test2.c
{{{
ym24@bio001:~$ mpicc -o test2 test2.c
}}}
 * 用 mpiexec 執行 test2 程式
{{{
ym24@bio001:~$ mpiexec -n 12 ./test2
}}}

== 範例三：test3.c ==
[[PageOutline]]

 * here is test3.c
{{{
ym24@bio001:~$ cat << EOF > test3.c
/* Program:
 *   每個 node 將訊息傳送給 node 0，由，node 0 統一印出
 * History:
 *   2008-06-12 BETA
 *   2008-06-17 更改顯示方式，並增加註解
 */

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

main(int argc, char **argv)
{
  int myrank, i, numprocs;
  char message[20];
  MPI_Status status;
  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
  MPI_Comm_rank(MPI_COMM_WORLD, &myrank);

  /* Node 0 will do the following */
  if(myrank == 0)
  {
    /* receive messages from other nodes */
    for(i = 1; i < numprocs; i++)
    {
      MPI_Recv(message, 20, MPI_CHAR, i, 99, MPI_COMM_WORLD, &status);
      printf("[Node 0] << 「%s」[Node %d] \n", message, status.MPI_SOURCE);
    }
  }

  /* other Nodes will do the following */
  if(myrank != 0)
  {
    /* send node's rank to Node 0 */
    sprintf(message, "[%d]", myrank);
    MPI_Send(message, 20, MPI_CHAR, 0, 99, MPI_COMM_WORLD);
    printf("[Node %d]「%s」 >> [Node 0]\n", myrank, message);
  }
  MPI_Finalize();
}
EOF
}}}
 * 用 mpicc 編譯 test3.c
{{{
ym24@bio001:~$ mpicc -o test2 test3.c
}}}
 * 用 mpiexec 執行 test3 程式
{{{
ym24@bio001:~$ mpiexec -n 12 ./test3
}}}

== 範例四：test4.c ==

[[PageOutline]]

 * here is test4
{{{
ym24@bio001:~$ cat << EOF > test4.c
/* Program:
 *   mpich_example 內建範例，計算 pi 。
 * History:
 *   2008-04-11 BETA
 *   2008-06-19 增加可重複輸入欲計算之精準度
 *   2008-06-23 加入 MPI_Barrier 以確保每個 node 在接受 n 後才執行
 */

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

double f( double );
double f( double a )
{
    return (4.0 / (1.0 + a*a));
}

int main( int argc, char *argv[])
{
    int done = 0, n, myid, numprocs, i=0;
    double PI25DT = 3.141592653589793238462643;
    double mypi, pi, h, sum, x;
    double startwtime = 0.0, endwtime;
    int  namelen;
    char processor_name[MPI_MAX_PROCESSOR_NAME];
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);
    MPI_Get_processor_name(processor_name,&namelen);
    fprintf(stderr,"Process %d on %s\n",
            myid, processor_name);
    n = 0;
    while (!done)
    {
        /* 由 node 0 將使用者輸入的值送給其它的 node  */
        if (myid == 0)
        {
            printf("Enter the number of intervals: (0 quits) ");
            scanf("%d", &n);
            startwtime = MPI_Wtime();
        }

        /* 這非常重要，所有的 node 必需在此同步，才可以收到使用者輸入的 n */
        MPI_Barrier(MPI_COMM_WORLD);

        /* 將 n 送給其它的 node  */
        MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);
        if (n == 0)
            done = 1;
        else
        {

            /* 此為計算 pi 的演算法 */
            h   = 1.0 / (double) n;
            sum = 0.0;
            for (i = myid + 1; i <= n; i += numprocs)
            {
                x = h * ((double)i - 0.5);
                sum += f(x);
            }
            mypi = h * sum;

            /* 將算完的結果傳給 node 0 加總 */
            MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
            if (myid == 0)
            {
                printf("pi is approximately %.16f, Error is %.16f\n",
                       pi, fabs(pi - PI25DT));
                endwtime = MPI_Wtime();
                printf("wall clock time = %f\n",
                       endwtime-startwtime);
            }
        }
    }
    MPI_Finalize();
    return 0;
}
EOF
}}}
 * 用 mpicc 編譯 test4.c
{{{
ym24@bio001:~$ mpicc -o test2 test4.c
}}}
 * 用 mpiexec 執行 test4 程式
{{{
ym24@bio001:~$ mpiexec -n 12 ./test4
}}}