[petsc-users] Increasing parallel speed-up

[Matthew Knepley]

On Mon, Jul 4, 2011 at 7:32 PM, Haren, S.W. van (Steven) <vanharen at nrg.eu>wrote:

> Thank you for you reply Jed.
>
> I will take a look at the preconditioners, to see if I can increase the
> scaling.
>
> CPU is an Intel i7 q720, just a standard laptop CPU.
>

As Jed points out, you will see very little speedup here due to the quite
poor memory subsystem. Intel
rarely points out that this setup is great for factoring, but lousy for
large swaths of computational science:

  http://www.mcs.anl.gov/petsc/petsc-as/documentation/faq.html#computers

     Matt


> Regards,
>
> Steven
>
>
>
> ---------------------------
> Date: Mon, 4 Jul 2011 12:24:56 -0500
> From: Jed Brown <jedbrown at mcs.anl.gov>
> Subject: Re: [petsc-users] Increasing parallel speed-up
> To: PETSc users list <petsc-users at mcs.anl.gov>
> Message-ID:
>        <CAM9tzSnBAmOdwxKEz-_BA9o+SvQHP69eEE50ozQ3LVFor0eSBQ at mail.gmail.com
> >
> Content-Type: text/plain; charset="utf-8"
>
> On Mon, Jul 4, 2011 at 12:09, Haren, S.W. van (Steven) <vanharen at nrg.eu
> >wrote:
>
> > one of the ksp solvers (Conjugate Gradient method with ILU(0)
> > preconditioning) gives poor parallel performance for the
> >
>
> We need to identify how much the poor scaling is due to the preconditioner
> changing (e.g. block Jacobi with ILU(0)) such that more iterations are
> needed versus memory bandwidth. Run with -ksp_monitor or
> -ksp_converged_reason to see the iterations. You can try -pc_type asm (or
> algebraic multigrid using third-party libraries) to improve the iteration
> count.
>
> If you want help seeing what's going on, send -log_summary output for each
> case.
>
>
> > following settings:
> >
> > - number of unknowns ~ 2 million
> > - 1, 2 and 4 processors (quad core CPU)
> >
>
> What kind? In particular, what memory bus and how many channels? Sparse
> matrix kernels are overwhelmingly limited by memory performance, so extra
> cores do very little good unless the memory system is very good (or the
> matrix fits in cache).
>
>
>


-- 
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110704/3659c875/attachment.htm>