bug#47218: glibc 2.33's HWCAPS and GCC Function Multiversioning for performance

bug#47218: glibc 2.33's HWCAPS and GCC Function Multiversioning for performance

[Léo Le Bouter via Bug reports for GNU Guix]

[-- Attachment #1: Type: text/plain, Size: 678 bytes --]

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

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

bug#47218: glibc 2.33's HWCAPS and GCC Function Multiversioning for performance

[Ludovic Courtès]

Hi Léo,

Léo Le Bouter <lle-bout@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’.