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From: "Ludovic Courtès" <ludovic.courtes@inria.fr>
To: zimoun <zimon.toutoune@gmail.com>
Cc: guix-devel@gnu.org
Subject: Re: build system option to allow CPU optimizations?
Date: Sun, 28 Nov 2021 18:36:57 +0100	[thread overview]
Message-ID: <87sfvg9o7a.fsf@gnu.org> (raw)
In-Reply-To: <86o867u6e1.fsf@gmail.com> (zimoun's message of "Fri, 26 Nov 2021 01:07:02 +0100")

Hi,

zimoun <zimon.toutoune@gmail.com> skribis:

> On Wed, 24 Nov 2021 at 13:10, Ricardo Wurmus <rekado@elephly.net> wrote:
>
>> The build phases that patch out these features would have to check 
>> for that build system option, much like they check the TESTS? 
>> option before attempting to run tests.
>
> Then it could be a transformation.   The idea sounds good to me.

I’ve been working on it last week with my HPC hat on.

To be clear, I think in may cases, passing ‘-march’ like you suggest is
the wrong approach; instead software should use (and usually does use)
function multi-versioning:

  https://hpc.guix.info/blog/2018/01/pre-built-binaries-vs-performance/

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!

Thanks,
Ludo’.


  reply	other threads:[~2021-11-28 17:37 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-24 12:10 build system option to allow CPU optimizations? Ricardo Wurmus
2021-11-26  0:07 ` zimoun
2021-11-28 17:36   ` Ludovic Courtès [this message]
2021-11-28 18:20     ` Ricardo Wurmus
2021-12-20 17:40       ` Ludovic Courtès
2021-12-14  3:36     ` Maxim Cournoyer

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