** Project changed: intel => linux
** Also affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu)
Status: New => Triaged
** Changed in: linux (Ubuntu)
Importance: Undecided => Medium
** Changed in: linux (Ubuntu)
Assignee: (unassigned) => Canonical Kernel Team (canonical-kernel-team)
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https://bugs.launchpad.net/bugs/1727136
Title:
[GLIBC] Fix glibc AVX frequency problems
Status in Linux:
Triaged
Status in linux package in Ubuntu:
Triaged
Bug description:
Various glibc versions use AVX512 or AVX incorrectly in memcpy/memset or use
AVX unintentionally due to branch mispredictions. On SKX using AVX can lower
the frequency by several bins.
There was a decision to not use AVX in memcpy/memset to avoid these problems
for legacy code.
glibc mainline has been fixed. The actual state per version depends on the
version, and what backports it has applied.
See the attachment for the fix status for several glibc versions. Need to
figure out for each supported glibc release if they are affected, and submit
backports of the fixes.
How to test:
Non AVX test code like compiles should not report any LVL1,2 AVX licenses with
perf stat -e
cpu/event=0x28,umask=0x18,name=core_power_lvl1_turbo_license/,cpu/event=0x28,umask=0x20,name=core_power_lvl2_turbo_license/,cpu/event=0x28,umask=0x40,name=core_power_throttle/,cycles
-a -I 1000 sleep 10
17.10 also hit this issue, when testing, need run some others application.
For example, building kernel.
16.04 hit the issue.
Target Release: 16.04
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