From: Joel Fernandes <joelaf@google.com>
To: Doug Anderson <dianders@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: RT_GROUP_SCHED throttling blocks unthrottled RT tasks?
Date: Fri, 5 Nov 2021 19:04:00 -0400 [thread overview]
Message-ID: <CAJWu+orNotdFUe0Bc9ooP+1nzajd=7A9WiSWXwtrsLkWi8gFAg@mail.gmail.com> (raw)
In-Reply-To: <CAD=FV=UKyJLhDEKxhqrit16kvLfi+g0DyYKL6bLJ35fO7NCTsg@mail.gmail.com>
On Fri, Nov 5, 2021 at 1:44 PM Doug Anderson <dianders@chromium.org> wrote:
[..]
>
>
> I tried gathering some tracing. One bit that might (?) be relevant:
>
> cros_ec_spi_hig-179 [000] d.h5 1495.305919: sched_waking:
> comm=kworker/4:2 pid=5232 prio=120 target_cpu=004
> cros_ec_spi_hig-179 [000] d.h6 1495.305926: sched_wakeup:
> comm=kworker/4:2 pid=5232 prio=120 target_cpu=004
> <idle>-0 [001] d.H5 1495.309113: sched_waking:
> comm=sugov:6 pid=2658 prio=-1 target_cpu=006
> <idle>-0 [001] d.H6 1495.309119: sched_wakeup:
> comm=sugov:6 pid=2658 prio=-1 target_cpu=006
> cros_ec_spi_hig-179 [000] d.h5 1495.309336: sched_waking:
> comm=sugov:6 pid=2658 prio=-1 target_cpu=006
> cros_ec_spi_hig-179 [000] d.h6 1495.309341: sched_wakeup:
> comm=sugov:6 pid=2658 prio=-1 target_cpu=006
> <idle>-0 [001] d.H5 1495.312137: sched_waking:
> comm=sugov:6 pid=2658 prio=-1 target_cpu=006
> <idle>-0 [001] d.H6 1495.312142: sched_wakeup:
> comm=sugov:6 pid=2658 prio=-1 target_cpu=006
> cros_ec_spi_hig-179 [000] d.h5 1495.312859: sched_waking:
> comm=sugov:6 pid=2658 prio=-1 target_cpu=006
> cros_ec_spi_hig-179 [000] d.h6 1495.312870: sched_wakeup:
> comm=sugov:6 pid=2658 prio=-1 target_cpu=006
>
> My best guess is that there's some bug in the scheduler where it just
> loops constantly picking an unthrottled RT task but then incorrectly
> decides that it's throttled and thus doesn't run it.
Thanks for posting this. Tricky bit indeed. I was wondering if the
issue is here:
https://elixir.bootlin.com/linux/latest/source/kernel/sched/rt.c#L1031
Basically, if something is actively getting RT-throttled on a CPU,
then if something else unthrottled but RT is ready to run, the
scheduler does resched_curr(rq) anyway. This probably happens when
update_curr_rt() is called on the unthrottled RT task via
task_tick_rt(). That seems a limitation of the current RT scheduler
I think? Thoughts?
next prev parent reply other threads:[~2021-11-05 23:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-05 17:44 RT_GROUP_SCHED throttling blocks unthrottled RT tasks? Doug Anderson
2021-11-05 23:04 ` Joel Fernandes [this message]
2021-11-05 23:05 ` Joel Fernandes
2021-11-05 23:10 ` Joel Fernandes
2021-11-16 1:13 ` Doug Anderson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAJWu+orNotdFUe0Bc9ooP+1nzajd=7A9WiSWXwtrsLkWi8gFAg@mail.gmail.com' \
--to=joelaf@google.com \
--cc=dianders@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).