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Subject: [OMPI users] Question about MPI_Barrier
From: Storm Zhang (stormzhg_at_[hidden])
Date: 2010-10-20 17:51:44


Dear all,

I got confused with my recent C++ MPI program's behavior. I have an MPI
program in which I use clock() to measure the time spent between to
MPI_Barrier, just like this:

MPI::COMM_WORLD.Barrier();
if if(rank == master) t1 = clock();
"code A";
 MPI::COMM_WORLD.Barrier();
if if(rank == master) t2 = clock();
"code B";

I need to measure t2-t1 to see the time spent on the code A between these
two MPI_Barriers. I notice that if I comment code B, the time seems much
less the original time (almost half). How does it happen? What is a possible
reason for it? I have no idea.

Thanks for your help.

Linbao