Bug#875618: openblas: please enable build on s390x

[Sébastien Villemot]

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On Mon, Sep 18, 2017 at 01:56:23PM +0200, Sébastien Villemot wrote:
> On Thu, Sep 14, 2017 at 12:34:34PM +0200, Christian Borntraeger wrote:
> > On 09/14/2017 09:58 AM, Sébastien Villemot wrote:
> > > On Wed, Sep 13, 2017 at 08:33:08PM +0000, PICCA Frederic-Emmanuel wrote:
> > >>> Unfortunately it does not look that simple. OpenBLAS is optimized for z13, but
> > >>> our s390x port is supposed to support all the z systems (see [1]).
> > >>
> > >> what about asking for a a z13-support package to the isa-support (source
> > >> package) maintainer. This way it could be possible to upload an optimise
> > >> vesion of openblas which can install on recent enought s390x machines.
> > > 
> > > I am not totally convinced by this solution. If we adopt it, somebody who
> > > installs e.g. octave on an old system-z machine will be hit by a failure in the
> > > dpkg installation process, which needs manual intervention. This is likely to
> > > generate problems in automated installers (and also confuse and annoy system
> > > admins).
> > > 
> > >> the question will be then : does the buildd support these instructions ?
> > > 
> > > I leave that to the s390 porters to answer.
> > 
> > FWIW, some years ago I did the atlas port for s390x. For dynamic linking the atlas
> > build/package process did support the exploitation of ELF HW_CAPS. So you could 
> > build a z900 (generic) and a z13 variant which is then picked by the linker at 
> > runtime. No idea if openblas allows the same. Of course the static variant (.a) 
> > must be the generic one.
> 
> Thanks for your feedback. I have opened a request upstream about the need for a
> z900 kernel, and for a dynamic selection between the z900 and z13 kernels
> (as OpenBLAS currently does on x86).

It turns out that there is already a support for generic System z, I had
overlooked that.

I have therefore pushed a changeset that builds a generic s390x binary.

However, upstream does not currently provide runtime detection, so owners of a
z13 system will have to recompile locally (as explained in README.Debian) in
order to get the best out of OpenBLAS (note that this is the same situation as
all the non-x86 archs).

-- 
⢀⣴⠾⠻⢶⣦⠀  Sébastien Villemot
⣾⠁⢠⠒⠀⣿⡁  Debian Developer
⢿⡄⠘⠷⠚⠋⠀  http://sebastien.villemot.name
⠈⠳⣄⠀⠀⠀⠀  http://www.debian.org
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