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Subject: Re: [OMPI devel] Progress of the asynchronous messages
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2008-11-06 15:04:13


For the web archives: this same question was posted and answered on
the users list. See this thread:

     http://www.open-mpi.org/community/lists/users/2008/11/7222.php

On Nov 6, 2008, at 1:00 PM, vladimir marjanovic wrote:

>> I am new user of Open MPI, I've used MPICH before.
>> I've tried on the user list but they couldn't help me.
>>
>> There is performance bug with the following scenario:
>>
>> proc_B: MPI_Isend(...,proc_A,..,&request)
>> do{
>> sleep(1);
>> MPI_Test(..,&flag,&request);
>> count++
>> }while(!flag);
>>
>> proc_A: MPI_Recv(...,proc_B);
>>
>> For message size 8MB, proc_B calls MPI_Test 88 times. It means
>> that point to point communication costs 88 seconds.
>> Btw, bandwidth isn't the problem (interconnection network:
>> InfiniBand)
>>
>> Obviously, there is the problem with progress of the asynchronous
>> messages. In order to overlap communication and computation I
>> don't want to use MPI_Wait. Probably, the message is being
>> decomposed into chucks and the size of chuck is probably defined by
>> environment variable.
>>
>> How can I advance the message more aggressively or can I control
>> size of chunk?
>> Thank you very much
>>
>> Vladimir
>
>
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-- 
Jeff Squyres
Cisco Systems