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syslog.py: report when ceph works are stuck #1945

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@lxbsz lxbsz commented May 23, 2024

Usually there will be performance bug when hitting the works are stuck:

workqueue: delayed_work [ceph] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND

URL: https://www.spinics.net/lists/ceph-users/msg78775.html

@lxbsz lxbsz requested review from vshankar, batrick and idryomov May 23, 2024 05:24
@@ -107,7 +107,7 @@ def syslog(ctx, config):
stdout = rem.sh(
[
'egrep', '--binary-files=text',
'\\bBUG\\b|\\bINFO\\b|\\bDEADLOCK\\b',
'\\bBUG\\b|\\bINFO\\b|\\bDEADLOCK\\b|\\bceph\\b.*\\bWQ_UNBOUND\\b',
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[Sun Sep 10 07:19:00 2023] workqueue: delayed_work [ceph] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND
[Sun Sep 10 08:41:24 2023] workqueue: ceph_con_workfn [libceph] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND

This regex would match only the first message (ceph), but not the second (libceph).

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Also, I wouldn't cling to WQ_UNBOUND -- it's an implementation detail that could change. If the concern is work items taking longer than expected to run, it would probably be better to match on "workqueue: ... hogged CPU for ...".

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[Sun Sep 10 07:19:00 2023] workqueue: delayed_work [ceph] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND
[Sun Sep 10 08:41:24 2023] workqueue: ceph_con_workfn [libceph] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND

This regex would match only the first message (ceph), but not the second (libceph).

Okay, let me run the test again.

Also, I wouldn't cling to WQ_UNBOUND -- it's an implementation detail that could change. If the concern is work items taking longer than expected to run, it would probably be better to match on "workqueue: ... hogged CPU for ...".

I just want to match the ceph ones, this will match all the possible warnings, is that okay ?

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I just want to match the ceph ones

That is totally fine -- I just wanted to say that we shouldn't be matching on name of the internal flag.

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idryomov commented May 23, 2024

Usually there will be performance bug when hitting the works are stuck:

workqueue: delayed_work [ceph] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND

This doesn't mean that the work item is stuck -- just that it's taking longer than a configurable threshold.

BTW WQ_UNBOUND is not a universal cure either -- it can lead to higher latencies:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c25da5b7baf1d243e6612ba2b97e2a2c4a1376f6
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f959325e6ac3f499450088b8d9c626d1177be160

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lxbsz commented May 28, 2024

Usually there will be performance bug when hitting the works are stuck:
workqueue: delayed_work [ceph] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND

This doesn't mean that the work item is stuck -- just that it's taking longer than a configurable threshold.

BTW WQ_UNBOUND is not a universal cure either -- it can lead to higher latencies:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c25da5b7baf1d243e6612ba2b97e2a2c4a1376f6 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f959325e6ac3f499450088b8d9c626d1177be160

Yeah, you are right. Just this warning could give us a hint that this code could be improved.

Usually there will be performance bug when hitting the works are
stuck:

workqueue: delayed_work [ceph] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND

URL: https://www.spinics.net/lists/ceph-users/msg78775.html
Signed-off-by: Xiubo Li <[email protected]>
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