[petsc-users] Amortizing calls to PetscOptionsFindPair_Private()

[Matthew Knepley]

On Sun, Jan 17, 2016 at 10:13 AM, Griffith, Boyce Eugene <
boyceg at email.unc.edu> wrote:

> Barry --
>
> Another random thought --- are these smallish direct solves things that
> make sense to (try to) offload to a GPU?
>

Possibly, but the only clear-cut wins are for BLAS3, so we would need to
stack up the identical solves.

  Matt


> Thanks,
>
> -- Boyce
>
> > On Jan 16, 2016, at 10:46 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >
> >  Boyce,
> >
> >   Of course anything is possible in software. But I expect an
> optimization to not rebuild common submatrices/factorization requires a
> custom PCSetUp_ASM() rather than some PETSc option that we could add
> (especially if you are using Matt's PC_COMPOSITE_MULTIPLICATIVE).
> >
> >   I would start by copying PCSetUp_ASM(), stripping out all the setup
> stuff that doesn't relate to your code and then mark identical domains so
> you don't need to call MatGetSubMatrices() on those domains and don't
> create a new KSP for each one of those subdomains (but reuses a common
> one). The PCApply_ASM() should be hopefully be reusable so long as you have
> created the full array of KSP objects (some of which will be common). If
> you increase the reference counts of the common KSP in
> > PCSetUp_ASM() (and maybe the common sub matrices) then the
> PCDestroy_ASM() should also work unchanged
> >
> > Good luck,
> >
> >  Barry
> >
> >> On Jan 16, 2016, at 8:25 PM, Griffith, Boyce Eugene <
> boyceg at email.unc.edu> wrote:
> >>
> >>
> >>> On Jan 16, 2016, at 7:00 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >>>
> >>>
> >>> Ok, I looked at your results in hpcviewer and don't see any surprises.
> The PETSc time is in the little LU factorizations, the LU solves and the
> matrix-vector products as it should be. Not much can be done on speeding
> these except running on machines with high memory bandwidth.
> >>
> >> Looks like LU factorizations are about 25% for this particular case.
> Many of these little subsystems are going to be identical (many will
> correspond to constant coefficient Stokes), and it is fairly easy to figure
> out which are which.  How hard would it be to modify PCASM to allow for the
> specification of one or more "default" KSPs that can be used for specified
> blocks?
> >>
> >> Of course, we'll also look into tweaking the subdomain solves --- it
> may not even be necessary to do exact subdomain solves to get reasonable MG
> performance.
> >>
> >> -- Boyce
> >>
> >>> If you are using the master branch of PETSc two users gave us a nifty
> new profiler that is "PETSc style" but shows the hierarchy of PETSc solvers
> time and flop etc. You can run with -log_view :filename.xml:ascii_xml and
> then open the file with a browser (for example open -f Safari filename.xml)
> or email the file.
> >>>
> >>> Barry
> >>>
> >>>> On Jan 16, 2016, at 5:09 PM, Bhalla, Amneet Pal S <
> amneetb at live.unc.edu> wrote:
> >>>>
> >>>>
> >>>>
> >>>>> On Jan 16, 2016, at 1:13 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >>>>>
> >>>>> Either way is fine so long as I don't have to install a ton of
> stuff; which it sounds like I won’t.
> >>>>
> >>>> http://hpctoolkit.org/download/hpcviewer/
> >>>>
> >>>> Unzip HPCViewer for MacOSX with command line and drag the unzipped
> folder to Applications. You will be able to
> >>>> fire HPCViewer from LaunchPad. Point it to this attached directory.
> You will be able to see three different kind of profiling
> >>>> under Calling Context View, Callers View and Flat View.
> >>>>
> >>>>
> >>>>
> >>>> <hpctoolkit-main2d-database.zip>
> >>>>
> >>>
> >>
> >
>
>


-- 
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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