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Re: Octave 3.6.0 on Windows XP plot fails.
From: |
Martin Helm |
Subject: |
Re: Octave 3.6.0 on Windows XP plot fails. |
Date: |
Wed, 29 Feb 2012 16:09:53 +0100 |
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KMail/1.13.6 (Linux/2.6.37.6-0.11-desktop; KDE/4.6.0; x86_64; ; ) |
Am Mittwoch, 29. Februar 2012, 16:01:57 schrieb Michael Goffioul:
> On Wed, Feb 29, 2012 at 2:28 PM, Martin Helm <address@hidden> wrote:
> > Am 29.02.2012 14:45, schrieb Xianyi Zhang:
> >> Hi,
> >>
> >> The matrix multiplication cannot obtain the performance from
> >> hyperthreading.
> >>
> >> Thanks
> >>
> >> Xianyi
> >
> > Why not? Is this a limitation of the mingw compiler, the windows
> > environment or the BLAS library in question?
>
> No, I think it's because of the principle of hyperthreading. HT does
> not mean you magically have 4 independent cores out of 2. You still
> have only 2 physical cores, but some parts of each core are duplicated
> such that they can appear as 4 instead of 2 at the OS level. However,
> the processing unit is not duplicated: so within a single physical
> core, each logical CPU will have to wait its turn on the processing
> unit.
>
> So roughly, if you have 4 operations that you can perform in parallel,
> only 2 will be done really simultaneously.
>
> HT can increase performances when you have 2 threads, one of which is
> stuck for some reason (waiting for data for instance). Then the other
> thread can use the processing unit while the first one is waiting. But
> if the 2 threads need the processing unit at the same time, you won't
> gain anything.
>
> So I think that what Xianyi Zhang means is that matrix multiplication
> is this kind of operations that cannot really benefit from HT. For the
> record, I've tried a 2-threaded ATLAS on a P4-HT (1 physical CPU, 2
> logical CPUs) and the performances were lower than a single-threaded
> one.
>
> Michael.
Performing now my previous trivial example on my atom netbook (dual core atom
with hyperthreading, htop shows 4 threads are used) ATLAS gives me a speedup
by a factor 2.4 (so more than double!) when using multi vs single threaded
atlas.
- Re: Octave 3.6.0 on Windows XP plot fails., (continued)
- Re: Octave 3.6.0 on Windows XP plot fails., nitnit, 2012/02/27
- Re: Octave 3.6.0 on Windows XP plot fails., maiky76, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., nitnit, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., maiky76, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., Xianyi Zhang, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., Martin Helm, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., Michael Goffioul, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails.,
Martin Helm <=
- Re: Octave 3.6.0 on Windows XP plot fails., Michael Goffioul, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., Martin Helm, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., Michael Goffioul, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., Martin Helm, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., Martin Helm, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., José Luis García Pallero, 2012/02/29
- Re: Octave 3.6.0 on Windows XP plot fails., Przemek Klosowski, 2012/02/29
Re: Octave 3.6.0 on Windows XP plot fails., Tatsuro MATSUOKA, 2012/02/15