[petsc-dev] PetscObjectViewFromOptions() pull request 1005 1006

[Lisandro Dalcin]

On Thu, 28 Jun 2018 at 20:17, Lawrence Mitchell <wence at gmx.li> wrote:
>
>
> OK, I've done some more benchmarking now, and cooked up a very simple test case.  I just solve a tiny problem 10 million times.
>
> On master, this completes on my machine in:
>
> If I leave the viewers on, this takes ages:
>
> (master-viewers-on) $ time taskset -c 1 ./many-ksps
> real 0m37.07s
>
> When I turn the viewers off
> (master-viewers-off) $ time taskset -c 1 ./many-ksps
> real 0m17.979s
>
> On knepley/feature-pc-patch both are faster, with no difference between turning viewers on and turning viewers off.
>
> (patch) $ time task set -c 1 ./many-ksps
> real 0m12.512s
>
> So a 25%-30% win.
>

Your example is hardly representative of any actual problem you will
ever solve with PCPATCH. You matrix is diagonal (identity!!), and the
same KSP object (and trivial matrix, and ILU preconditioner) is used
over and over again (all memory will reside in cache?), and all the
solves are just one iteration. The fact that you get an improvement in
Matt's branch respect to turning the viewers off smells to just C
function call overhead, otherwise how do you explain the difference?


-- 
Lisandro Dalcin
============
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