mpi use c language

MPI use C language (1)

Speaker ：呂宗螢Adviser ：梁文耀　老師Date ： 2006/10/27

Embedded and Parallel Systems Lab

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Outline

MPI Introduction 撰寫程式和執行的步驟撰寫平行程式的基本觀念 MPI 一些基本 function MPI function 的基本架構

MPI_COMM_WORLD MPI point to point 的傳送

Blocking Non-blocking

Message passing 規則


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Outline

Communication mode Standard Synchronous Buffered Ready

Blocking Message Passing Hello.c

Non-Blocking Message Passing Wait Test Isend-Irecv.c


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MPI Introduction

MPI ， Message Passing Interface 適用於平行運算環境，定義了 process 和 process 之間傳送訊息的一

個標準，不止是單一電腦內的 process 和 process 傳送訊息，還可以在網路上不同電腦間的 process 與 process 的溝通。

目的是希望能提供一套可移值性和高效率的傳送訊息的標準，其內容包含了分散式記憶體（ Distributed-Memory ）和共享式記憶體( Shared-Memory) 架構。

有相同功能的是 PVM (Parallel Virtual Machine) ，但現在一般較多人使用的是 MPI 。

MPICH2


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撰寫程式和執行的步驟

1. 啟動MPI環境mpdboot -n 4 -f mpd.hosts

2. 撰寫MPI程式vi hello.c

3. Compilempicc hello.c –o hello.o 　

4. 執行程式mpiexec –n 4 ./hello.o

5. 結束MPImpdallexit


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撰寫平行程式的基本觀念

需由程式設計師來規畫平行化程式


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並不是只要將程式平行化之後就能提高程式的效率


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MPI 程式基本架構 #include "mpi.h"

MPI_Init();

Do some work or MPI functionexample: MPI_Send() / MPI_Recv()

MPI_Finalize();


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MPI一些基本 function

int MPI_Init( int *argc, char *argv[]) 必須在所有 MPI function 前使用初始 MPI_COMM_WORLD 和 MPI_COMM_SELF 指令參數 (argc, argv) 複製到所有 process

int MPI_Comm_rank ( MPI_Comm comm, int *rank) 取得 process 自己的 process ID Rank = Process ID

double MPI_Wtime() 傳回一個時間代表目前時間

int MPI_Finzlize() 結束 MPI 執行環境，在所有工作完成後必須呼叫

int MPI_Abort(MPI_Comm comm, int errorcode)

結束所有 MPI 行程，並強制結束程式


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MPI一些基本 function

MPI_COMM_WORLD 是一個 communicator ，主要作用是指出辨別所有有加入平行運算環

境的 Processes ，而 process 和 process 溝通時所使用的 function call 都要用他做為參數，才能讓 process 互相找到 process 做溝通。


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MPI function的基本架構

其回傳值就是用來判斷 MPI function 是不是成功的完成只有 double MPI_Wtime() 和 double MPI_Wtick() 兩個 function 例外。

int result;result= MPI-function();

function int MPI_Comm_size( MPI_Comm comm, int *size)

功能取得總共有多少 process數在該 communicator

parameters comm ： IN ， MPI_COMM_WORLDsize ： OUT，總計 process數目

return value int：如果執行成功回傳MPI_SUCCESS，０


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MPI function的一些錯誤回傳值

MPI_SUCCESS MPI function 成功完成，沒有錯誤

MPI_ERR_COMM Communicator 錯誤，或是 Communicator 是 NULL

MPI_ERR_COUNT Count 參數錯誤

MPI_ERR_TYPE 錯誤的資料型態 (Datatype) ，可能是使用非 MPI 定義

的 Datatype

MPI_ERR_BUFFER buffer 錯誤

MPI_ERR_ROOT 錯誤的 root ，是指 Rank(ID) 不是 communicator 內的，

通常是 >0 && < communicator’ size


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MPI point to point 的傳送

Blocking

Non-Blocking

Send MPI_Send(buffer, count, datatype, dest, tag, comm)

Receive MPI_Recv(buffer, count, datatype, source, tag, comm, status)

Send MPI_Isend(buffer, count, datatype, dest, tag, comm, request)

Receive MPI_Irecv(buffer, count, datatype, source, tag, comm, request)


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MPI_Status

typedef struct MPI_Status {

int count;

int cancelled;

int MPI_SOURCE; // 來源 ID

int MPI_TAG; // 來源傳送的 tag

int MPI_ERROR; // 錯誤控制碼 } MPI_Status;


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MPICH 實作的方法


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Blocking


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Non-Blocking


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Message passing 規則在傳訊接收訊息時，MPI可以保證順序性

如果有兩個 Send 成功傳送了兩個訊息 a 和 b ，那接收者 B ，開始接收訊息時，一定先收到 a 再收到 b 。

如果有兩個 Receive ， a 和 b 同時在接收時，那可能會接收到同一個Send 的訊息，但 a 一定會在 b 之前接收到。

但是如果是一個multiple threads的程式就沒辦法保證了。另外就是在如果 process 0 要傳送給 process 2 ，同時 process 1 也

要傳送給 process ，而 process 只有一個 receive 的動作時，只有一個 process 的傳送動作會成功完成


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DataTypeC

MPI_CHAR signed char

MPI_SHORT signed short int

MPI_INT signed int

MPI_LONG signed long int

MPI_UNSIGNED_CHAR unsigned char

MPI_UNSIGNED_SHORT unsigned short int

MPI_UNSIGNED unsigned int

MPI_UNSIGNED_LONG unsigned long int

MPI_FLOAT float

MPI_DOUBLE double

MPI_LONG_DOUBLE long double

MPI_BYTE 8 binary digits

MPI_PACKED data packed or unpacked with MPI_Pack()/ MPI_Unopack()


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Communication mode

Standard Synchronous Buffered Ready


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Standard mode


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Synchronous mode


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Buffered mode


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Ready mode


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Blocking Message Passing

int MPI_Send(void* buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm)

int MPI_Recv(void* buf, int count, MPI_Datatype datatype, int source, int tag, MPI_Comm comm, MPI_Status *status)

int MPI_Ssend(void* buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm)


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Blocking Message Passing

int MPI_Bsend(void* buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm) int MPI_Buffer_attach(void* buffer_addr, int* size) int MPI_Buffer_detach(void* buffer_addr, int* size)

int MPI_Rsend(void* buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm)

int MPI_Get_count(MPI_Status *status, MPI_Datatype datatype, int *count)


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First program Hello.c

目的：產生兩個 Process ，利用 blocking 方式，互相

傳送訊息，並且計算在傳送接收的時間


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hello.c#include "mpi.h"#include <stdio.h>#define SIZE 20

int main(int argc,char *argv[]){ int numtasks, rank, dest, source, rc, count, tag=1; char inmsg[SIZE]; char outmsg[SIZE];

double starttime, endtime; MPI_Status Stat; MPI_Datatype strtype;

MPI_Init(&argc,&argv); //起始MPI環境 MPI_Comm_rank(MPI_COMM_WORLD, &rank); //取得自己的 process ID

MPI_Type_contiguous(SIZE, MPI_CHAR, &strtype); //設定新的資料型態 string MPI_Type_commit(&strtype); 　 //建立新的資料型態 string

starttune=MPI_Wtime(); //取得目前時間


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hello.c if (rank == 0) { dest = 1; source = 1; strcpy(outmsg,"Who are you?");

//傳送訊息到 process 0 rc = MPI_Send(outmsg, 1, strtype, dest, tag, MPI_COMM_WORLD); printf("process %d has sended message: %s\n",rank, outmsg);

//接收來自 process 1 的訊息 rc = MPI_Recv(inmsg, 1, strtype, source, tag, MPI_COMM_WORLD, &Stat); printf("process %d has received: %s\n",rank, inmsg); } else if (rank == 1) { dest = 0; source = 0; strcpy(outmsg,"I am process 1"); rc = MPI_Recv(inmsg, 1, strtype, source, tag, MPI_COMM_WORLD, &Stat); printf("process %d has received: %s\n",rank, inmsg); rc = MPI_Send(outmsg, 1 , strtype, dest, tag, MPI_COMM_WORLD); printf("process %d has sended message: %s\n",rank, outmsg); }


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hello.c

endtime=MPI_Wtime(); // 取得結束時間//使用MPI_CHAR來計算實際收到多少資料

rc = MPI_Get_count(&Stat, MPI_CHAR, &count); printf("Task %d: Received %d char(s) from task %d with tag %d and use

time is %f \n", rank, count, Stat.MPI_SOURCE, Stat.MPI_TAG, endtime-starttime);

MPI_Type_free(&strtype); //釋放 string資料型態 MPI_Finalize(); //結束MPI}

1. Compilempicc hello.c –o hello.o 　

2. 執行程式mpiexec –n 4 ./hello.o


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hello.c 執行結果

process 0 has sended message: Who are you? process 1 has received: Who are you? process 1 has sended message: I am process 1 Task 1: Received 20 char(s) from task 0 with tag 1 and use time is

0.001302 process 0 has received: I am process 1 Task 0: Received 20 char(s) from task 1 with tag 1 and use time is

0.002133


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Non-blocking Message Passing

int MPI_Isend(void* buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm, MPI_Request *request)

int MPI_Irecv(void* buf, int count, MPI_Datatype datatype, int source, int tag, MPI_Comm comm, MPI_Request *request)

int MPI_Issend(void* buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm, MPI_Request *request)

int MPI_Ibsend(void* buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm, MPI_Request *request)

int MPI_Irsend(void* buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm, MPI_Request *request)


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Wait

int MPI_Wait(MPI_Request *request, MPI_Status *status)

int MPI_Waitall(int count, MPI_Request *array_of_requests, MPI_Status *array_of_statuses)

int MPI_Waitany(int count, MPI_Request *array_of_requests, int *index, MPI_Status *status)

int MPI_Waitsome(int incount, MPI_Request *array_of_requests, int *outcount, int *array_of_indices, MPI_Status *array_of_statuses)


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Test

int MPI_Test(MPI_Request *request, int *flag, MPI_Status *status)

int MPI_Testall(int count, MPI_Request *array_of_requests, int *flag, MPI_Status *array_of_statuses)

int MPI_Testany(int count, MPI_Request *array_of_requests, int *index, int *flag, MPI_Status *status)

int MPI_Testsome(int incount, MPI_Request *array_of_requests, int *outcount, int *array_of_indices, MPI_Status *array_of_statuses)


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Isend-Irecv.c

目的：每個 process 會去 receive 上一個和下一個

process ID 的 send每個 process 會去 send 訊息給上一個和下一

個 process利用 non-blocking並且測試 non-blocking 的動作是否完成


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Isend-Irecv.c

#include “mpi.h”#include <stdio.h>int main(int argc,char *argv[]){ int numtasks, rank, next, prev, buf[2], tag1=1, tag2=2; MPI_Request reqs[4]; MPI_Status stats[4]; int flag; MPI_Init(&argc,&argv); MPI_Comm_size(MPI_COMM_WORLD, &numtasks); MPI_Comm_rank(MPI_COMM_WORLD, &rank); prev = rank-1; next = rank+1; if (rank == 0) prev = numtasks - 1; if (rank == (numtasks - 1)) next = 0;


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Isend-Irecv.c

//使用 non-blocking 的 receive的接收來算上個 process的資料 ,並將 handle存進reqs[0] MPI_Irecv(&buf[0], 1, MPI_INT, prev, tag1, MPI_COMM_WORLD, &reqs[0]);

MPI_Irecv(&buf[1], 1, MPI_INT, next, tag2, MPI_COMM_WORLD, &reqs[1]);//使用 non-blocking 的 send傳送到上個 process,並將 handle存進 reqs[2]

MPI_Isend(&rank, 1, MPI_INT, prev, tag2, MPI_COMM_WORLD, &reqs[2]); MPI_Isend(&rank, 1, MPI_INT, next, tag1, MPI_COMM_WORLD, &reqs[3]); MPI_Waitall(4, reqs, stats); //等待所有在 reqs內的 handle完成

MPI_Test(&reqs[0],&flag, &stats[0]); //第一個MPI_Irecv是否完成 printf("Process %d: has receive data %d from prevenient process %d\n", rank, buf[0], prev); printf("Process %d: has receive data %d from next process %d\n", rank, buf[1],

prev); printf("Process %d: test %d\n",rank , flag); MPI_Finalize();}


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Isend-Irecv.c 執行結果 Process 2: has receive data 1 from prevenient process 1 Process 2: has receive data 3 from next process 1 Process 2: test 1 Process 0: has receive data 3 from prevenient process 3 Process 0: has receive data 1 from next process 3 Process 0: test 1 Process 1: has receive data 0 from prevenient process 0 Process 1: has receive data 2 from next process 0 Process 1: test 1 Process 3: has receive data 2 from prevenient process 2 Process 3: has receive data 0 from next process 2 Process 3: test 1


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The End

Thank you very much!

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