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Subject: Re: [OMPI users] Question about MPI_Barrier
From: Storm Zhang (stormzhg_at_[hidden])
Date: 2010-10-21 09:24:38


Thanks for your suggestion. I am trying MPI_Wtime to see if there is any
difference.

Linbao

On Thu, Oct 21, 2010 at 1:37 AM, jody <jody.xha_at_[hidden]> wrote:

> Hi
>
> I don't know the reason for the strange behaviour, but anyway,
> to measure time in an MPI application you should use MPI_Wtime(), not
> clock()
>
> regards
> jody
>
> On Wed, Oct 20, 2010 at 11:51 PM, Storm Zhang <stormzhg_at_[hidden]> wrote:
> > 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
> > _______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
> >
>
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