[mpich-discuss] MPI_Send/Recv vs MPI_un/pack performance

[Roberto Fichera]

William Gropp ha scritto:
> Roberto,
>
> Pack and Unpack were provided for applications that were used to the 
> PVM style of building messages - as others have mentioned, MPI 
> provided datatypes to permit a good MPI implementation to optimize the 
> handling of non-contiguous data.
Ok! I see, thanks a lot.
>
> Bill
>
> On Jul 31, 2008, at 12:18 PM, Roberto Fichera wrote:
>
>> Hi All on the list,
>>
>> My apologies if this argument was already well discussed many times
>> before in the list, but playing around the
>> MPI_Send() and MPI_Recv() I end up on trying to optimize both transfert
>> and receive parts for our
>> serialization/deserialization functions. So looking around I decide to
>> use the MPI_Pack() and MPI_Unpack() into
>> an already allocated buffer and send/receive it in one "big shot". After
>> getting it working I finally created a test program
>> for profiling the performances in both cases. My results was quite
>> stunning, working with various sizes in Mb of serialized
>> data, the MPI_Send() is ~2 to 4 times faster than paired MPI_Pack() &
>> MPI_Send()!!! So, my understanding for the
>> MPI_Pack() is that it can be usefull for packing and unpacking data to
>> send/receive for performance reasons, maybe
>> do I'm missing something (o.s. tuning)?
>>
>> I'm using mpich2 v1.0.7 with channel ch3:socket on Fedora 8 x86_64.
>>
>> Best regards,
>> Roberto Fichera.
>>
>> <char.png><double.png><int.png>
>
> William Gropp
> Paul and Cynthia Saylor Professor of Computer Science
> University of Illinois Urbana-Champaign
>
>

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