Re: fftw runtime cpu detection

[Eric Bavier <bavier@cray.com>]

On Fri, Apr 06, 2018 at 10:05:43AM +0200, Ludovic Courtès wrote:
> Hello Eric,
> 
> Eric Bavier <bavier@cray.com> skribis:
> 
> > I recently discovered that the FFTW library can do runtime cpu
> > detection.  In order to do this, the package needs to be configured to
> > build SIMD "codelets", like how our 'fftw-avx' currently does.  Then,
> > based on the instruction support detected at runtime, make those
> > kernels available to the fftw "planner" for execution.
> 
> That’s really good news!  Thanks for testing it.
> 
> The patch LGTM.  Can you confirm that the planner won’t ever try to use
> the AVX2 codelets, for instance when running the test suite on an x86_64
> box that lacks AVX2?

Yes, I've successfully run 'make check' on an sse2-only machine where
'--enable-avx' and '--enable-avx2' where configured.  I'll check on an
i686 machine tonight.

> If that’s the case, I’d be in favor of pushing this patch to core-updates.

Great.  I'll do some more testing.  Should I send a finalized patch to
guix-patches when it's ready?

-- 
Eric Bavier, Scientific Libraries, Cray Inc.