GNU bug report logs - #47218
glibc 2.33's HWCAPS and GCC Function Multiversioning for performance

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Léo Le Bouter <lle-bout <at> zaclys.net>
To: bug-guix <at> gnu.org
Subject: glibc 2.33's HWCAPS and GCC Function Multiversioning for performance
Date: Wed, 17 Mar 2021 19:59:51 +0100

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Hello!

Please see:
- 
https://www.gnu.org/software/libc/manual/html_mono/libc.html#Hardware-Capability-Tunables
- https://www.phoronix.com/scan.php?page=news_item&px=glibc-hwcaps-RFC
- https://gcc.gnu.org/onlinedocs/gcc/Function-Multiversioning.html

This could help GNU Guix create binaries that include multiple code
paths for several CPU features in the same binary and selecting the
best at runtime when the binary is run.

It is the best fit for GNU Guix because it means we can still use
substitutes and profit from specialized optimizations without
parameterized packages or each user adding "-march=native" to CFLAGS
(breaking reproducibility).

Léo

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Message #8 received at 47218 <at> debbugs.gnu.org (full text, mbox):

From: Ludovic Courtès <ludovic.courtes <at> inria.fr>
To: Léo Le Bouter <lle-bout <at> zaclys.net>
Cc: 47218 <at> debbugs.gnu.org
Subject: Re: bug#47218: glibc 2.33's HWCAPS and GCC Function Multiversioning
 for performance
Date: Thu, 18 Mar 2021 14:17:42 +0100

Hi Léo,

Léo Le Bouter <lle-bout <at> zaclys.net> skribis:

> Please see:
> - 
> https://www.gnu.org/software/libc/manual/html_mono/libc.html#Hardware-Capability-Tunables
> - https://www.phoronix.com/scan.php?page=news_item&px=glibc-hwcaps-RFC
> - https://gcc.gnu.org/onlinedocs/gcc/Function-Multiversioning.html
>
> This could help GNU Guix create binaries that include multiple code
> paths for several CPU features in the same binary and selecting the
> best at runtime when the binary is run.
>
> It is the best fit for GNU Guix because it means we can still use
> substitutes and profit from specialized optimizations without
> parameterized packages or each user adding "-march=native" to CFLAGS
> (breaking reproducibility).

For the record, we are well aware of these features and follow this very
closely in particular in the context of Guix-HPC:

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

It seems to me that this bug report is not actionable though.  Unless
there are concrete steps you’d like to suggest, I propose to close this
issue.

Thanks,
Ludo’.

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