[英]Limits with MPI_Send or MPI_Recv?
Do we have any limits about message size on MPI_Send
or MPI_Recv
- or limits by computer? 我们对
MPI_Send
或MPI_Recv
上的邮件大小有任何限制吗?还是受计算机限制? When I try to send large data, it can not completed. 当我尝试发送大数据时,它无法完成。 This is my code:
这是我的代码:
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
#include <math.h>
#include <string.h>
void AllGather_ring(void* data, int count, MPI_Datatype datatype,MPI_Comm communicator)
{
int me;
MPI_Comm_rank(communicator, &me);
int world_size;
MPI_Comm_size(communicator, &world_size);
int next=me+1;
if(next>=world_size)
next=0;
int prev=me-1;
if(prev<0)
prev=world_size-1;
int i,curi=me;
for(i=0;i<world_size-1;i++)
{
MPI_Send(data+curi*sizeof(int)*count, count, datatype, next, 0, communicator);
curi=curi-1;
if(curi<0)
curi=world_size-1;
MPI_Recv(data+curi*sizeof(int)*count, count, datatype, prev, 0, communicator, MPI_STATUS_IGNORE);
}
}
void test(void* buff,int world_size,int count)
{
MPI_Barrier(MPI_COMM_WORLD);
AllGather_ring(buff,count,MPI_INT,MPI_COMM_WORLD);
MPI_Barrier(MPI_COMM_WORLD);
}
}
void main(int argc, char* argv[]) {
int count = 20000;
char processor_name[MPI_MAX_PROCESSOR_NAME];
MPI_Init(&argc,&argv);
int world_rank,world_size,namelen;
MPI_Comm_size(MPI_COMM_WORLD, &world_size);
MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
int* buff=(int*) malloc(world_size*sizeof(int)*count);
int i;
for (i = 0; i < world_size; i++) {
buff[i]=world_rank;
}
test(buff,world_size,count);
MPI_Finalize();
}
It stopped when I try to run with a buffer about 80000 bytes (40000 integers) (by count = 20000 + 4 processes) 当我尝试使用大约80000字节(40000整数)的缓冲区运行时,它停止了(按计数= 20000 + 4个进程)
You code is incorrect. 您的代码不正确。 You are posting the receives only after the respective sends are completed.
仅在完成各自的发送后才过帐接收。
MPI_Send
is only guaranteed to complete after a corresponding MPI_Recv
is posted, so you run into a classic deadlock. 只有在发布相应的
MPI_Recv
之后,才能保证MPI_Send
完成,因此您会遇到经典的死锁。
It happens to work for small messages, because they are handled differently (using an unexpected message buffer as performance optimization). 它恰好适用于小消息,因为它们的处理方式不同(使用意外的消息缓冲区作为性能优化)。 In that case
MPI_Send
is allowed to complete before the MPI_Recv
is posted. 在这种情况下,允许在发布
MPI_Recv
之前完成MPI_Send
。
Alternatively you can: 或者,您可以:
MPI_Isend
, MPI_Irecv
) to resolve the deadlock. MPI_Isend
, MPI_Irecv
)以解决死锁。 MPI_Sendrecv
. MPI_Sendrecv
。 MPI_Allgather
. MPI_Allgather
。 I recommend the latter. 我推荐后者。
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