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Re: [Help-gsl] Question about GSL performance under OpenMP

From: Pedro Gardete
Subject: Re: [Help-gsl] Question about GSL performance under OpenMP
Date: Thu, 6 Oct 2011 10:40:02 -0700

Hi Brian,

Thanks for your answer. I can rule out most of the possibilities, but it's
good to know the GSL behaves under OpenMP. Maybe my code is not cooperating
somehow, so I'll try a simpler case and see what happens.

Thanks again,

On Thu, Oct 6, 2011 at 9:46 AM, Brian Hawkins <address@hidden>wrote:

> Hi Pedro,
> In my experience the design of GSL is very amenable to parallelism, and I
> would be quite surprised if it was causing problems.
> However, it's pretty common to scale up a program to n threads and get less
> than a factor of n speed up.  It depends a lot on what the code is doing
> and
> what kind of hardware you've got.  There are also some issues related to
> OpenMP threading itself.  A quick guess is that maybe some of your
> equations
> solve much faster than others, so you might want to add "schedule(dynamic)"
> to the pragma before your loop.
> Regards,
> Brian
> On Thu, Oct 6, 2011 at 9:00 AM, <address@hidden> wrote:
> >
> > Date: Wed, 5 Oct 2011 18:20:38 -0700
> > From: Pedro Gardete <address@hidden>
> >
> > Hi,
> >
> > I need to go through many systems of equations, which I'm using
> > the gsl_multiroot_fsolver_hybrid method to solve for. The systems solve
> > fine, but when I put them inside an OpenMP loop (each thread solves one
> > system at a time and stores the result) the performance invariably comes
> > down for each thread as I add more. Should this be expected given that
> the
> > threads are independent (ie, don't wait for each other)?
> >
> > Thanks,
> > Pedro
> >
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