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.
On Thu, Oct 21, 2010 at 5:17 AM, Jeff Squyres <email@example.com>
On Oct 20, 2010, at 5:51 PM, Storm Zhang wrote: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:
> 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.
- 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?
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