Re: build system option to allow CPU optimizations?

["Ludovic Courtès" <ludo@gnu.org>]

Hi,

Ricardo Wurmus <rekado@elephly.net> skribis:

> Ludovic Courtès <ludovic.courtes@inria.fr> writes:

[...]

> It may very well be the wrong approach in principle, but I also think
> that it’s a neat escape hatch for specific use cases. Separating
> reproducibility patching makes the package transformation mechanism
> more powerful and appealing.  Much like respecting TESTS? makes it
> easy for users of modified packages to bypass a failing test suite,
> making patching of Makefiles to remove CPU tuning conditional would
> make for much less complex custom package definitions.
>
>> I found one case though where this is not possible: C++ header-only
>> libraries such as Eigen contain hand-optimized vectorized routines,
>> selected at build time, but we end up compiling Eigen users as the
>> x86_64/AArch64 baseline, which is a waste.  (If you do know of other
>> problematic cases, I’m interested in taking a look!)
>>
>> My solution to that is “package multi-versioning” via a
>> transformation
>> option.  Hopefully I’ll submit preliminary patches within a week or
>> so!
>
> Oh, exciting!

I forgot to mention it here, but it’s available for testing and probably
even ready to merge:

  https://issues.guix.gnu.org/52283

I think it makes an option to dismiss ‘-march’ removal unnecessary; or,
put differently, it achieves the same.

I’m interested in seeing which packages people would mark as “tunable”
and what performance gains it gives!

Thanks,
Ludo’.