[lttng-dev] ***UNCHECKED*** Re: Re: urcu workqueue thread uses 99% of cpu while workqueue is empty

Mathieu Desnoyers mathieu.desnoyers at efficios.com
Wed Jun 22 09:19:58 EDT 2022

----- On Jun 22, 2022, at 3:45 AM, Minlan Wang wangminlan at szsandstone.com wrote:


Hi Minlan,

> --
> And the lttng session is configured to trace these events:
> kernel: syscall futex

On the kernel side, in addition to the syscall futex, I would really like to see what
happens in the scheduler, mainly the wait/wakeup tracepoints. This can be added by using:

lttng enable-event -k 'sched_*'

This should help us confirm whether we indeed have a situation where queued wake ups
happen to wake up a wait happening only later, which is unexpected by the current liburcu
userspace code.


> ---
> The babletrace output of this session is pretty big, 6 MB in size, i put it in
> the attachment trace_0622.tar.bz2.
> Let my know if your mailbox can't handle such big attachment.

It would be even better if you can share the binary trace, because then it's easy to
load it in trace compass, cut away time ranges that don't matter, and lots of other
useful stuff.



Mathieu Desnoyers
EfficiOS Inc.

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