[gmx-developers] replica-exchange and MPI_Sendrecv

Mark Abraham Mark.Abraham at anu.edu.au
Mon Dec 7 06:50:34 CET 2009


I can see in release-4-0-patches src/kernel/repl_ex.c that use of 
MPI_Sendrecv is commented out, and replaced by Isend-Recv-Wait 
combinations. While either should work correctly, Sendrecv is in routine 
use in the DD and PME code, so why not here too? If Sendrecv is 
unsuitable for some reason I don't appreciate, Irecv-Send-Wait is often 
a better combination for cyclic messaging, because many MPI libraries do 
better if the receive is already posted when the send is called, because 
no buffering is required. It may seem like a small thing, but it might 
add up to noticeable expense in the kind of massively-parallel scenario 
you can get with long REMD simulations.



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