[mpich-discuss] measuring time in mpi program

[Gus Correa]

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