From: Quentin Perret <qperret@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@redhat.com, vincent.guittot@linaro.org,
dietmar.eggemann@arm.com, qais.yousef@arm.com,
rickyiu@google.com, wvw@google.com, patrick.bellasi@matbug.net,
xuewen.yan94@gmail.com, linux-kernel@vger.kernel.org,
kernel-team@android.com
Subject: Re: [PATCH v2 1/3] sched: Fix UCLAMP_FLAG_IDLE setting
Date: Fri, 11 Jun 2021 07:25:42 +0000 [thread overview]
Message-ID: <YMMP9uqcCeDlt95F@google.com> (raw)
In-Reply-To: <YMJiaO0IN2pN/EYY@hirez.programming.kicks-ass.net>
On Thursday 10 Jun 2021 at 21:05:12 (+0200), Peter Zijlstra wrote:
> On Thu, Jun 10, 2021 at 03:13:04PM +0000, Quentin Perret wrote:
> > The UCLAMP_FLAG_IDLE flag is set on a runqueue when dequeueing the last
> > active task to maintain the last uclamp.max and prevent blocked util
> > from suddenly becoming visible.
> >
> > However, there is an asymmetry in how the flag is set and cleared which
> > can lead to having the flag set whilst there are active tasks on the rq.
> > Specifically, the flag is cleared in the uclamp_rq_inc() path, which is
> > called at enqueue time, but set in uclamp_rq_dec_id() which is called
> > both when dequeueing a task _and_ in the update_uclamp_active() path. As
> > a result, when both uclamp_rq_{dec,ind}_id() are called from
> > update_uclamp_active(), the flag ends up being set but not cleared,
> > hence leaving the runqueue in a broken state.
> >
> > Fix this by setting the flag in the uclamp_rq_inc_id() path to ensure
> > things remain symmetrical.
>
> The code you moved is neither in uclamp_rq_inc_id(), although
> uclamp_idle_reset() is called from there
Yep, that is what I was trying to say.
> nor does it _set_ the flag.
Ahem. That I don't have a good excuse for ...
>
> I'm thinking it's been a long warm day? ;-)
Indeed :-)
Let me have another cup of coffee and try to write this again.
Thanks,
Quentin
next prev parent reply other threads:[~2021-06-11 7:27 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-10 15:13 [PATCH v2 0/3] A few uclamp fixes Quentin Perret
2021-06-10 15:13 ` [PATCH v2 1/3] sched: Fix UCLAMP_FLAG_IDLE setting Quentin Perret
2021-06-10 19:05 ` Peter Zijlstra
2021-06-11 7:25 ` Quentin Perret [this message]
2021-06-17 15:27 ` Dietmar Eggemann
2021-06-21 10:57 ` Quentin Perret
2021-06-10 15:13 ` [PATCH v2 2/3] sched: Skip priority checks with SCHED_FLAG_KEEP_PARAMS Quentin Perret
2021-06-10 19:15 ` Peter Zijlstra
2021-06-11 8:59 ` Quentin Perret
2021-06-11 9:07 ` Quentin Perret
2021-06-11 9:20 ` Peter Zijlstra
2021-06-10 15:13 ` [PATCH v2 3/3] sched: Make uclamp changes depend on CAP_SYS_NICE Quentin Perret
2021-06-11 12:48 ` Qais Yousef
2021-06-11 13:08 ` Quentin Perret
2021-06-11 13:26 ` Qais Yousef
2021-06-11 13:49 ` Quentin Perret
2021-06-11 14:17 ` Qais Yousef
2021-06-11 14:43 ` Quentin Perret
2021-06-14 15:03 ` Qais Yousef
2021-06-21 10:52 ` Quentin Perret
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=YMMP9uqcCeDlt95F@google.com \
--to=qperret@google.com \
--cc=dietmar.eggemann@arm.com \
--cc=kernel-team@android.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=patrick.bellasi@matbug.net \
--cc=peterz@infradead.org \
--cc=qais.yousef@arm.com \
--cc=rickyiu@google.com \
--cc=vincent.guittot@linaro.org \
--cc=wvw@google.com \
--cc=xuewen.yan94@gmail.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.