[mpich-discuss] measuring time in mpi program

[Jain, Rohit]

Thanks.
Rohit

On Feb 25, 2011, at 20:23, "Gus Correa" <gus at ldeo.columbia.edu> wrote:

> Gus Correa wrote:
>> Jain, Rohit wrote:
>>> Is there any performance data on using MPI_WTime()? How much time does
>>> it typically take?
>>> 
>>> We have lot of 'wait-send' and 'wait-receive' code at lot of places, and
>>> we need to measure time spent in this sections. We currently use
>>> gettimeofday() function to measure this time. Would MPI_WTime be faster
>>> than that?
>>> 
>>> Regards,
>>> Rohit
>>> 
>>> 
>>> -----Original Message-----
>>> From: mpich-discuss-bounces at mcs.anl.gov
>>> [mailto:mpich-discuss-bounces at mcs.anl.gov] On Behalf Of Gus Correa
>>> Sent: Friday, February 25, 2011 10:49 AM
>>> To: Mpich Discuss
>>> Subject: Re: [mpich-discuss] measuring time in mpi program
>>> 
>>> hatem Elshazly wrote:
>>>> hey guys,
>>>> 
>>>> does anybody know how to measure execution time of mpi program?
>>>> is there any option we can append in the mpirun\mpiexec command to measure time?
>>>> is there any time command that measure clock cycle time, execution time,etc..?
>>>> 
>>>> 
>>>> thank u very much
>>>> hatem
>>>> 
>>>> 
>>>> 
>>> 
>>> Hi Hatem
>>> 
>>> The standard outline is something like this:
>>> 
>>> ... initialize your MPI environment ...
>>> start=MPI_Wtime()
>>> ... do your work (including MPI calls)...
>>> end=MPI_Wtime()
>>> if (myrank .eq. 0) then
>>>   print *, "Time spent (in seconds) is: ", end - start
>>> endif
>>> ... finalize MPI ...
>>> 
>>> (You could also print the results from all ranks, if you want.)
>>> 
>>> I my experience, perfomance tends to be quite variable if you don't have
>>> a 'critical mass' of "do your work", i.e., if you do just a
>>> couple of send/recv and get out.  Works better if your MPI calls
>>> are on a loop in "do your work".
>>> 
>>> I hope this helps.
>>> Gus Correa
>>> 
>>> PS - It looks like you managed to troubleshoot your network problems.
>>> I hope so.
>>> You never got back to the list on that subject.
>> Hi Rohit
>> I did a quick look at src/mpi/timer/mpidtime.c in MPICH2 1.3.1.
>> You can check by yourself.
>> It seems to me that MPI_WTime wraps gettimeofday.
>> (For portability, perhaps?)
>> The MPICH2 developers may clarify.
>> Gus Correa
> 
> Oops!
> I just saw that Pavan already answered your question, Rohit.
> Gus Correa
> 
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