From: Joel Fernandes <joel@joelfernandes.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Valentin Schneider <vschneid@redhat.com>,
Vineeth Pillai <vineethrp@google.com>,
Suleiman Souhlal <suleiman@google.com>,
Hsin Yi <hsinyi@google.com>,
Frederic Weisbecker <frederic@kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH RFC] sched/fair: Avoid unnecessary IPIs for ILB
Date: Tue, 10 Oct 2023 13:55:00 -0400 [thread overview]
Message-ID: <CAEXW_YSJTShQoOCdTOHamatV2VFFpK5=GZ40=he5Egz5TRBMkg@mail.gmail.com> (raw)
In-Reply-To: <ZSPjIwWxSdKAsKZD@gmail.com>
On Mon, Oct 9, 2023 at 7:25 AM Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Joel Fernandes <joel@joelfernandes.org> wrote:
>
> > > > Fixes: 7fd7a9e0caba ("sched/fair: Trigger nohz.next_balance updates when a CPU goes NOHZ-idle")
> > >
> > > Hurm.. does this really warrant a Fixes tag? Afaict nothing is currently
> > > broken -- this is a pure optimization question, no?
> >
> > IMHO it is a breakage as it breaks NOHZ -- a lot of times the ILB kicks
> > back the CPU stopping the tick out of idle (effectively breaking NOHZ).
> > The large number of IPIs also wrecks power and it happens only on 6.1 and
> > after. Having the fixes tag means it will also goto all stable kernels >=
> > 6.1. Hope that sounds reasonable and thank you for taking a look!
>
> So it's basically a fix of a NOHZ performance regression, introduced by
> 7fd7a9e0caba or so, correct?
Yes.
> As long as the fixes have a good hope of being backported with a low amount
> of overhead, a Fixes: tag for a ~2 years old performance regression is
> unusual but not unprecedented.
>
> We just need to make sure we don't put too much of a burden on the
> shoulders of -stable maintainers ...
Sure, that sounds good. After we upstream, I am happy to assist in any
stable backporting work related to this as well. In any case, I have
to backport it to ChromeOS kernels which are based on stable. There's
only the 6.1 stable kernel at the moment that is affected.
thanks,
- Joel
next prev parent reply other threads:[~2023-10-10 17:55 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-05 16:17 [PATCH RFC] sched/fair: Avoid unnecessary IPIs for ILB Joel Fernandes (Google)
2023-10-06 10:51 ` Ingo Molnar
2023-10-06 16:32 ` Joel Fernandes
2023-10-08 17:35 ` Joel Fernandes
2023-10-09 18:33 ` Vineeth Pillai
2023-10-10 7:15 ` Vincent Guittot
2023-10-10 19:32 ` Joel Fernandes
2023-10-06 13:46 ` Vincent Guittot
2023-10-06 16:46 ` Joel Fernandes
2023-10-06 19:18 ` Shrikanth Hegde
2023-10-06 20:10 ` Shrikanth Hegde
2023-10-08 16:50 ` Joel Fernandes
2023-10-06 21:20 ` Vineeth Pillai
2023-10-08 16:46 ` Joel Fernandes
2023-10-06 20:01 ` Peter Zijlstra
2023-10-08 16:39 ` Joel Fernandes
2023-10-09 11:25 ` Ingo Molnar
2023-10-09 20:11 ` Steven Rostedt
2023-10-10 17:55 ` Joel Fernandes [this message]
2023-10-19 14:56 ` kernel test robot
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='CAEXW_YSJTShQoOCdTOHamatV2VFFpK5=GZ40=he5Egz5TRBMkg@mail.gmail.com' \
--to=joel@joelfernandes.org \
--cc=bristot@redhat.com \
--cc=bsegall@google.com \
--cc=dietmar.eggemann@arm.com \
--cc=frederic@kernel.org \
--cc=hsinyi@google.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@kernel.org \
--cc=mingo@redhat.com \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=suleiman@google.com \
--cc=vincent.guittot@linaro.org \
--cc=vineethrp@google.com \
--cc=vschneid@redhat.com \
/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).