[Numpy-discussion] Accelerate or OpenBLAS for numpy / scipy wheels?

[Ralf Gommers]

On Tue, Jun 28, 2016 at 2:55 PM, Matthew Brett <matthew.brett at gmail.com>
wrote:

> Hi,
>
> On Tue, Jun 28, 2016 at 5:25 AM, Charles R Harris
> <charlesr.harris at gmail.com> wrote:
> >
> >
> > On Mon, Jun 27, 2016 at 9:46 PM, Matthew Brett <matthew.brett at gmail.com>
> > wrote:
> >>
> >> Hi,
> >>
> >> I just succeeded in getting an automated dual arch build of numpy and
> >> scipy, using OpenBLAS.  See the last three build jobs in these two
> >> build matrices:
> >>
> >> https://travis-ci.org/matthew-brett/numpy-wheels/builds/140388119
> >> https://travis-ci.org/matthew-brett/scipy-wheels/builds/140684673
> >>
> >> Tests are passing on 32 and 64-bit.
> >>
> >> I didn't upload these to the usual Rackspace container at
> >> wheels.scipy.org to avoid confusion.
> >>
> >> So, I guess the question now is - should we switch to shipping
> >> OpenBLAS wheels for the next release of numpy and scipy?  Or should we
> >> stick with the Accelerate framework that comes with OSX?
> >>
> >> In favor of the Accelerate build : faster to build, it's what we've
> >> been doing thus far.
>

Faster to build isn't really an argument right? Should be the same build
time except for building OpenBLAS itself once per OpenBLAS version. And
only applies to building wheels for releases - nothing changes for source
builds done by users on OS X. If build time ever becomes a real issue, then
dropping the dual arch stuff is probably the way to go - the 32-bit builds
make very little sense these days.

What we've been doing thus far - that is the more important argument.
There's a risk in switching, we may encounter new bugs or lose some
performance in particular functions.


> >>
> >> In favor of OpenBLAS build : allows us to commit to one BLAS / LAPACK
> >> library cross platform,
>

This doesn't really matter too much imho, we have to support Accelerate
either way.


> when we have the Windows builds working.
> >> Faster to fix bugs with good support from main developer.  No
> >> multiprocessing crashes for Python 2.7.
>

This is probably the main reason to make the switch, if we decide to do
that.


>   I'm still a bit nervous about OpenBLAS, see
> > https://github.com/scipy/scipy/issues/6286. That was with version
> 0.2.18,
> > which is pretty recent.
>
> Well - we are committed to OpenBLAS already for the Linux wheels, so
> if that failure was due to an error in OpenBLAS, we'll have to report
> it and get it fixed / fix it ourselves upstream.
>

Indeed. And those wheels have been downloaded a lot already, without any
issues being reported.

I'm +0 on the proposal - the risk seems acceptable, but the reasons to make
the switch are also not super compelling.

Ralf
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