[petsc-users] Computation to communication ratio for PETSc's routines

[Matthew Knepley]

On Wed, Jun 13, 2012 at 6:45 PM, Alexander Grayver
<agrayver at gfz-potsdam.de>wrote:

> Hello,
>
> As stated, I would like to estimate computation to communication ratio for
> PETSc's linear algebra routines (e.g. MatMult{Transpose}, MatPtAP,
> MatMatMult etc.)
> As far as I understand the ratio depends on particular implementation and
> number of processes one runs application on.
> So I guess these formulas should be known?
>

It depends on the input data. For example, block diagonal matrices do not
communicate in MatMult().


> If not then I see one way to estimate it. Write app with those operations,
> parse -log_summary and then divide flops/messages, however the question is
> what information from -log_summary output should be used for that?
>

We give the number of messages and the average message length, so you can
get the total length across processes. Since
each side records, we divide by 2 (I think, you should check PetscLogView
for specifics). You can also use PetscLogViewPython()
to simplify parsing.

   Matt


> Thanks.
>
> --
> Regards,
> Alexander
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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