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

[Roberto Fichera]

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.

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