[Numpy-discussion] Windows, blas, atlas and dlls

[rif]

But I'd hope that the overhead for going through the wrappers is constant,
rather than dependent on the size, so that for large matrices you'd get
essentially equivalent performance?


On Mon, Feb 18, 2013 at 8:28 AM, Dag Sverre Seljebotn <
d.s.seljebotn at astro.uio.no> wrote:

> On 02/18/2013 05:26 PM, rif wrote:
> > I have no answer to the question, but I was curious as to why directly
> > calling the cblas would be 10x-20x slower in the first place.  That
> > seems surprising, although I'm just learning about python numerics.
>
> The statement was that directly (on the Cython level) calling cblas is
> 10x-20x slower than going through the (slow) SciPy wrapper routines.
> That makes a lot of sense if the matrices are smalle nough.
>
> Dag Sverre
>
> >
> >
> > On Mon, Feb 18, 2013 at 7:38 AM, Sergio Callegari
> > <sergio.callegari at gmail.com <mailto:sergio.callegari at gmail.com>> wrote:
> >
> >     Hi,
> >
> >     I have a project that includes a cython script which in turn does
> >     some direct
> >     access to a couple of cblas functions. This is necessary, since some
> >     matrix
> >     multiplications need to be done inside a tight loop that gets called
> >     thousands
> >     of times. Speedup wrt calling scipy.linalg.blas.cblas routines is
> >     10x to 20x.
> >
> >     Now, all this is very nice on linux where the setup script can
> >     assure that the
> >     cython code gets linked with the atlas dynamic library, which is the
> >     same
> >     library that numpy and scipy link to on this platform.
> >
> >     However, I now have trouble in providing easy ways to use my project
> in
> >     windows. All the free windows distros for scientific python that I
> have
> >     looked at (python(x,y) and winpython) seem to repackage the windows
> >     version of
> >     numpy/scipy as it is built in the numpy/scipy development sites.
> >     These appear
> >     to statically link atlas inside some pyd files.  So I get no atlas
> >     to link
> >     against, and I have to ship an additional pre-built atlas with my
> >     project.
> >
> >     All this seems somehow inconvenient.
> >
> >     In the end, when my code runs, due to static linking I get 3
> >     replicas of 2
> >     slightly different atlas libs in memory. One coming with
> >     _dotblas.pyd in numpy,
> >     another one with cblas.pyd or fblas.pyd in scipy. And the last one
> >     as the one
> >     shipped in my code.
> >
> >     Would it be possible to have a win distro of scipy which provides
> some
> >     pre built atlas dlls, and to have numpy and scipy dynamically link
> >     to them?
> >     This would save memory and also provide a decent blas to link to for
> >     things
> >     done in cython. But I believe there must be some problem since the
> >     scipy site
> >     says
> >
> >     "IMPORTANT: NumPy and SciPy in Windows can currently only make use
> >     of CBLAS and
> >     LAPACK as static libraries - DLLs are not supported."
> >
> >     Can someone please explain why or link to an explanation?
> >
> >     Unfortunately, not having a good, prebuilt and cheap blas
> >     implementation in
> >     windows is really striking me as a severe limitation, since you
> >     loose the
> >     ability to prototype in python/scipy and then move to C or Cython
> >     the major
> >     bottlenecks to achieve speed.
> >
> >     Many thanks in advance!
> >
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> >
> >
> >
> >
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