I'm unaware of any systems that support LSE that are also supported by
the hwe-{x,y,z} kernels. I'll therefore mark those as "Won't Fix" for
those releases. If someone is aware of such a system - and can take on
the testing of this change for those releases, we can reconsider.
** Changed in: linux (Ubuntu Xenial)
Status: Triaged => Won't Fix
** Changed in: linux (Ubuntu)
Status: In Progress => Fix Committed
** Changed in: linux (Ubuntu Yakkety)
Status: Triaged => Won't Fix
** Changed in: linux (Ubuntu Zesty)
Status: Triaged => Won't Fix
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https://bugs.launchpad.net/bugs/1691614
Title:
please enable CONFIG_ARM64_LSE_ATOMICS
Status in linux package in Ubuntu:
Fix Committed
Status in linux source package in Xenial:
Won't Fix
Status in linux source package in Yakkety:
Won't Fix
Status in linux source package in Zesty:
Won't Fix
Bug description:
[Impact]
Performance is lowered for ARM >= v8.1 cpus by not taking advantage of the
"Large System Extenstion" atomic instructions they provide.
Note: This config was enabled during xenial development, but was
disabled to workaround a FTBFS[*] due to us not having a new enough
binutils to support it. binutils was later updated in xenial, and
supports these instructions.
[Test Case]
grep CONFIG_ARM64_LSE_ATOMICS=y /boot/config-$(uname -r)
[Regression Risk]
There is a known small performance overhead for < ARMv8.1 arm64 systems
(noted in the Kconfig). To mitigate the risk of runtime or build failures, this
should be tested on both ARMv8 and >= ARMv8.1 systems, to exercise both code
paths.
[*] https://answers.launchpad.net/~canonical-kernel-
team/+archive/ubuntu/unstable/+build/8438034
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