Bug#1053241: glibc: please apply upstream patch to fix slow fstat

[Fabio Pedretti]

Package: glibc
Version: 2.36-9+deb12u1
Severity: normal
X-Debbugs-Cc: pedrett...@gmail.com

Dear Maintainer,

glibc uses a slow version of fstat. Details are documented
here: https://lwn.net/Articles/944214/

A patch to fix this was merged in glibc:
https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=551101e8240b7514fc646d1722f8b79c90362b8f

The patch applies cleanly and builds fine also on bookworm glibc.
Please consider apply it to fix slow fstat.

Thanks.

[Aurelien Jarno]

Hi,

This patch changes the syscall used by binaries, so it has to be
considered with a lot of care in a stable release, it could break
existing seccomp filters. In any case it has to live a few months in
testing/unstable first.

Note that the kernel patch that improves the performance of fstatat, has
not been merge to the upstream stable tree, nor to bookworm.

In order to better understand the need for this patch in bookworm, could
you please give some details about your workload and the performance
impact it has?

Regards
Aurelien

--
Aurelien Jarno GPG: 4096R/1DDD8C9B
aure...@aurel32.net http://aurel32.net

[Fabio Pedretti]

Il giorno dom 26 nov 2023 alle ore 16:28 Aurelien Jarno
<aur...@debian.org> ha scritto:

I did some test with my use case, borg backup with many unchanged
files, see https://github.com/borgbackup/borg/issues/4498 for some
background and system calls impact, where borg 1.2 slow downs a lot
vs. borg 1.1.

I checked using strace the patch, it did the job (newfstatat calls
were replaced with fstat), and I'd hoped that it would improve
performance, however my use case improved just marginally (difficult
to have reproducible data in my case, but it was like 5%).

I didn't notice any other regression, however.

I see the glibc patch is still only on 2.39, while even Debian
experimental has just 2.38.

The alternative kernel patch is in 6.6 (as you say, still not in Debian).

Given all of this, I agree we can wait to land it on trixie and leave
bookworm as is, so feel free to just close the issue in this case.

Thanks for your time.