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From: Rhys Ulerich <rhys.ulerich@gmail.com>
To: Maxime Boissonneault <maxime.boissonneault@calculquebec.ca>
Cc: gsl-discuss@sourceware.org
Subject: Re: Adding OpenMP support for some of the GSL functions
Date: Thu, 13 Dec 2012 16:44:00 -0000	[thread overview]
Message-ID: <CAKDqugTG9EybSGqkaZr0z2y79-af2sF3TWx2qUMbwMXaOAbezA@mail.gmail.com> (raw)
In-Reply-To: <CAKDqugQRt+q-V+Sv=AxmREwZAq1jFrGzU+xFmZi1YRQDSnXmfA@mail.gmail.com>

> This feels like you're getting a small
> memory/cache bandwidth increase for the rkf45_apply level-1-BLAS-like
> operations by using multiple cores but the cores are otherwise not
> being used effectively.  I say this because a state vector 1e6 doubles
> long will not generally fit in cache.  Adding more cores increases the
> amount of cache available.

Hmm... I tentatively take this back on re-thinking how you've added
the #pragma omp lines to the rkf45.c file you attached elsewhere in
this thread.  Try using a single
    #pragma omp parallel
and then individual lines like
    #pragma omp for
at each for loop.  Using
    #pragma omp parallel for
repeatedly as you've done can introduce excess overhead, depending on
your compiler, because it may incur unnecessary overhead.

- Rhys

  reply	other threads:[~2012-12-13 16:44 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-12-11 20:04 Maxime Boissonneault
2012-12-12 16:35 ` Frank Reininghaus
2012-12-12 21:11   ` Maxime Boissonneault
2012-12-12 21:41     ` Rhys Ulerich
2012-12-12 23:32       ` Maxime Boissonneault
2012-12-12 17:05 ` Rhys Ulerich
2012-12-12 21:13   ` Maxime Boissonneault
2012-12-12 21:36     ` Rhys Ulerich
2012-12-12 23:35       ` Maxime Boissonneault
2012-12-13  2:29         ` Rhys Ulerich
2012-12-13 13:22           ` Maxime Boissonneault
2012-12-13 15:53             ` Rhys Ulerich
2012-12-13 16:44               ` Rhys Ulerich [this message]
2012-12-13 21:07                 ` Maxime Boissonneault
2012-12-13 21:05               ` Maxime Boissonneault
2012-12-13 21:14                 ` Maxime Boissonneault

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