[Bug 1999551] Re: glibc: backport AArch64 mem{cpy,cmp} improvements

[Launchpad Bug Tracker]

This bug was fixed in the package glibc - 2.31-0ubuntu9.12

---------------
glibc (2.31-0ubuntu9.12) focal; urgency=medium

  * Drop SVE memcpy implementation due to kernel-related performance
    regression

glibc (2.31-0ubuntu9.11) focal; urgency=medium

  * Drop memcmp arm64 SIMD optimization patch due to performance regression
    on Raspberry Pi 3+ and 4

glibc (2.31-0ubuntu9.10) focal; urgency=medium

  [ Andrei Gherzan ]
  * d/p/lp1910312: Backport upstream fix for SEM_STAT_ANY (LP: #1910312)

  [ Simon Chopin ]
  * d/p/lp1999551/*: backport mem{cmp,cpy} optimizations for arm64 (LP: #1999551)
  * d/p/lp2001932/*: fix segfault in AVX2 strncmp (LP: #2001932)
  * d/p/lp2001975/*: fix overflow in AVX2 wcsncmp (LP: #2001975)

 -- Simon Chopin <schopin at ubuntu.com>  Wed, 26 Jul 2023 09:44:39 +0200

** Changed in: glibc (Ubuntu Focal)
       Status: Fix Committed => Fix Released

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Title:
  glibc: backport AArch64 mem{cpy,cmp} improvements

Status in glibc package in Ubuntu:
  Fix Released
Status in glibc source package in Focal:
  Fix Released
Status in glibc source package in Jammy:
  Triaged
Status in glibc source package in Kinetic:
  Fix Released

Bug description:
  [impact]

  There have been relatively recent improvements to the memcmp and
  memcpy routines for server-grade AArch64 implementation, in particular
  AWS's Graviton3.

  We'd like to backport those improvements to Jammy and Focal when
  appropriate, under the HWE umbrella.

  The relevant patches are

  https://sourceware.org/git/?p=glibc.git;a=commit;h=9f298bfe1f183804bb54b54ff9071afc0494906c (Jammy & Focal)
  https://sourceware.org/git/?p=glibc.git;a=commit;h=b51eb35c572b015641f03e3682c303f7631279b7 (Focal only, already present in Jammy)

  In addition, to be able to actually test the changes and its impact on
  all architectures, we'll need the following fix:

  https://sourceware.org/git/?p=glibc.git;a=commit;h=311a7e0256975275d97077f1af338bc9caf0c837

  [test case]

  Since those are optimization patches, we'll be relying on the
  autopkgtests triggered by the upload for regression detection.

  However, we'll also benchmark the optimizations on Graviton AWS
  instances as well as various Raspberry Pi models to ensure there is no
  severe performance regression on those platforms.

  To do the performance test, first install the libc from this PPA:

  https://launchpad.net/~schopin/+archive/ubuntu/glibc-benchmark

  that is the current Jammy glibc with the extra fix for benchmarking.

  Then, untar the attached archive bench-timing.tar.xz on the target
  platform, and follow the instructions from the README.

  [Regression potential]

  This could potentially impact performance on other, non-server-grade
  arm64 platforms such as RPi. Furthermore, there could be unforeseen
  issues with the newly optimized routine in edge cases (a recent amd64
  optimization had issues on page boundaries, for instance).

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