[Bug 1885012] Re: Provide libc6-lse binary package optimized for Large System Extensions (LSE)

[Steve Langasek]

Hello Balint, or anyone else affected,

Accepted glibc into bionic-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/glibc/2.27-3ubuntu1.3
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-
bionic to verification-done-bionic. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-bionic. 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.

** Changed in: glibc (Ubuntu Bionic)
       Status: New => Fix Committed

** Tags added: verification-needed verification-needed-bionic

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https://bugs.launchpad.net/bugs/1885012

Title:
  Provide libc6-lse binary package optimized for Large System Extensions
  (LSE)

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

Bug description:
  [Impact]

  * libc6 is not using LSE atomics even on capable HW causing poor
  performance in heavily threaded application

  [Test Case]

  * install libc6-lse on capable arm64
  * verify that the library is in use:
  $ strace -eopenat ls
  openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libselinux.so.1", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/atomics/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libpcre.so.3", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/atomics/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/atomics/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3
  * Compile and run the attached a.c test program and observe it running much faster on high (>= 8) core count capable HW than with the standard libc6 package.

  [Regression Potential]

  * The libraries in libc6-lse can't be run on not LSE capable HW and trying to use them results in crashes due to the illegal instructions. The fix includes proper checking for HW capabilities and selecting the libraries in /lib/aarch64-linux-gnu/atomics/ only when LSE instructions are supported.
  * The package build can also fail when trying to run tests of libc6-lse on not LSE capable HW but this is avoided by detecting LSE instructions and running the tests only if the HW supports them.
  * Initramfs-tools could break when generating intramfs when the new libc6-lse package is installed (LP: #1880853), but this regression is fixed in initramfs-tools and Breaks: is added against affected initramfs-tools versions.

  [Other Info]

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