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

[Matthew Knepley]

On Thu, Jun 14, 2012 at 3:09 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Jun 13, 2012, at 8:17 AM, Alexander Grayver wrote:
>
> > On 13.06.2012 13:24, Matthew Knepley wrote:
> >> 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.
> >
> > Is there total amount of flops given for different operations separately
> (I see max flops over all processes only)?
>
>    Sadly no. My original plan was that people who wanted different summary
> information would copy PetscLogView() and modify it to output just what
> they want. Sadly that may be too difficult.


You can back out the total flops from the flop rate and time.

   Matt


>
>   Barry
>
> >
> >>
> >>    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
> >
> >
> > --
> > 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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