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Subject: Re: [OMPI users] Question about MPI_Barrier
From: Storm Zhang (stormzhg_at_[hidden])
Date: 2010-10-21 09:24:54


Thanks a lot for your reply. By commenting code B, I mean if I remove the
code B part, then the time spent on code A seems to run faster. I do have a
lot of communications in code B too. It involves 500 procs. I had thought
code B should have no effect on the time spent on code A if I use
MPI_Barrier.

Linbao
On Thu, Oct 21, 2010 at 5:17 AM, Jeff Squyres <jsquyres_at_[hidden]> wrote:

> On Oct 20, 2010, at 5:51 PM, Storm Zhang wrote:
>
> > 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.
>
> I'm not sure what you're asking here -- do you mean that if you put some
> comments in code B, it takes much less time than if you don't put comments?
> If so, then the comments have nothing to do with the execution run-time --
> something else is going on that is causing the delay. Some questions:
>
> - how long does it take to execute code B -- microseconds, or seconds, or
> ...?
> - how many processes are involved?
> - what are you doing in code B; is it communication intensive and/or do you
> synchronize with other processes?
> - are you doing your timings on otherwise-empty machines?
>
> --
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
>
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