[Bug 1951032] Please test proposed package

[Steve Langasek]

Hello Michael, or anyone else affected,

Accepted glibc into focal-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/glibc/2.31-0ubuntu9.9
in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
focal to verification-done-focal. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-focal. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

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https://bugs.launchpad.net/bugs/1951032

Title:
  AArch64: Backport memcpy improvements

Status in glibc package in Ubuntu:
  Fix Released
Status in glibc source package in Focal:
  Fix Committed

Bug description:
  [impact]
  glibc 2.32 contained a number of improvements to the memcpy routines for server-grade AArch64 implementations (in particular, graviton2 & graviton3). They should be backported to focal, as the LTS releases are by far the most used on servers.

  [test case]
  Download the "bench.tar.gz" attachment from this report. It has a README
  that explains what to do, but here it is for reference:

  benchmark for testing arm64 memcpy improvements in SRU

  This is a benchmark that was derived from the memcpy benchmarks in glibc but altered to benchmark the public 'memcpy' symbol and be linked to the
  installed libc.

  To use this there are 5 steps:

  1. build -- just run "make test"
  2. run before upgrade -- "make bench-before"
  3. upgrade libc6 package -- depends on what is being tested!
  4. run again -- "make bench-after"
  5. compare -- "make compare"

  It produces output like this:

     length | before (MiB/s) |  after (MiB/s) |    delta
  ----------|----------------|----------------|----------
      32768 |         233.74 |         248.03 |    6.11%
      65536 |         443.72 |         468.69 |    5.63%
     131072 |         853.71 |         895.08 |    4.84%
     262144 |        1640.93 |        1718.91 |    4.75%
     524288 |        2501.80 |        2604.83 |    4.12%
    1048576 |        3896.77 |        4157.74 |    6.70%

  On graviton2 systems, this should show an improvement of at least
  several percent. On other arm64 systems (raspberry pis of various
  vintage, thunderx2, xgene, etc etc) no significant regression should
  be seen.

  [regression potential]
  Rebuilding glibc is always a little risky (toolchain bugs and incompatibilities between the old and new versions can be surprising). But the autopkgtests and some manual general testing can help here.

  For this specific change, there is a potential risk that the new
  memcpy implementation could be used on a system where it is not in
  fact the fastest. We should run the test case not only on the systems
  where it is expected to help, but other systems such as the RPi4 and
  the launchpad build farm to ensure performance is not regressed there.

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