** Changed in: linux (Ubuntu)
Status: Fix Committed => Fix Released
** Changed in: linux (Ubuntu Xenial)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1645449
Title:
Linux perf regression in 4.4.0-42 and newer
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Xenial:
Fix Released
Bug description:
There is a regression in the 4.4.0-42 kernel update that is still
present in the latest 4.4.0 update. I have verified that this appears
in Ubuntu 16.04 and Ubuntu 14.04 (with ubuntu-xenial kernel installed)
amd64. I also suspect this happens in default Ubuntu 16.10 kernel as
well, but i have not tested.
4.4.0-38 did not have this issue.
in 4.4.0-42 and newer, perf records incorrect timestamps which can be
verified by running this command:
$ perf record -a -e sched:sched_-k CLOCK_MONOTONIC switch stress -c 10000 -t
10
stress: info: [25560] dispatching hogs: 10000 cpu, 0 io, 0 vm, 0 hdd
stress: info: [25560] successful run completed in 6s
[ perf record: Woken up 16 times to write data ]
Warning:
78487 out of order events recorded.
Note that the warning about out of order events is a symptom of this problem
and is not expected to happen. This does not happen(correct behavior) if i run
4.4.0-38 and older, or if i run a fully patched upstream 4.4.35 kernel instead.
This regression has already been fixed upstream but has not been included in
ubuntu-xenial kernel yet.
Upstream fix is here:
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=78c7b55b362e868e529ab6579134708fcf5539dd
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