[petsc-users] Enquiry regarding log summary results

Jed Brown jedbrown at mcs.anl.gov
Mon Oct 8 13:37:18 CDT 2012

On Sun, Oct 7, 2012 at 4:45 PM, TAY wee-beng <zonexo at gmail.com> wrote:

>  Hi,
> I have attached 3 results using 12,24 and 32 processors. I am using a
> completely different clusters and I'm testing if it's the cluster
> configuration problems. It's seems that VecScatterEnd does not scale well
> from 12 to 24 to 32. Does these results show that there's problems with the
> partition still? My partition is clustered closely at the center, I'm
> wondering if this has a great effect on scaling...

Your partition is probably not well balanced, but you're also seeing what
happens when an algorithm is limited by bandwidth. The vendors tend not to
tell you that cores don't matter unless you can get memory to them. Sparse
linear algebra is heavily bandwidth-limited so you should not expect to see
speedup by using all cores on a node. If you use additional nodes, you will
get additional memory buses which are a better indicator of performance.
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