[petsc-users] Variable wall times

[Barry Smith]

   Also make sure you are doing consistent binding of MPI processes to cores:  see http://www.mcs.anl.gov/petsc/documentation/faq.html#computers  and run the streams benchmarks several times to see if you get consistent results.

   With no other user or system processes consuming large amounts of cycles and suitable binding you should get pretty consistent results.

  Barry



> On Feb 22, 2016, at 1:08 PM, Jed Brown <jed at jedbrown.org> wrote:
> 
> Phanisri Pradeep Pratapa <ppratapa at gatech.edu> writes:
> 
>> Hi,
>> 
>> I am trying to compare run times for a function in petsc using ksp solve.
>> When I run the code in parallel on a single node (64 processors), it seems
>> to take different wall time for each run, although run on exactly same
>> processors. For example one time it could take 10 sec where as the same run
>> next time could take 20 sec. (This happens for other choices of processors
>> too, not just 64)
> 
> You probably just have a noisy system.  It could be due to the
> architecture and system software or it could be caused by contention
> with other jobs and/or misconfiguration.
> 
> See this paper, especially Figure 1.
> 
> http://unixer.de/publications/img/hoefler-scientific-benchmarking.pdf