[petsc-users] Variable wall times

[Jed Brown]

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
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