linux-kernel - Re: [PATCH v4 0/2] Avoid spurious freezer wakeups

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Message-ID: <20230926200238.GB13828@noisy.programming.kicks-ass.net>
Date:   Tue, 26 Sep 2023 22:02:38 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Carlos Llamas <cmllamas@...gle.com>
Cc:     Elliot Berman <quic_eberman@...cinc.com>,
        Ingo Molnar <mingo@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>, kernel@...cinc.com,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org,
        Prakash Viswalingam <quic_prakashv@...cinc.com>
Subject: Re: [PATCH v4 0/2] Avoid spurious freezer wakeups

On Tue, Sep 26, 2023 at 04:17:33PM +0000, Carlos Llamas wrote:
> On Fri, Sep 08, 2023 at 03:49:14PM -0700, Elliot Berman wrote:
> > After commit f5d39b020809 ("freezer,sched: Rewrite core freezer logic"),
> > tasks that transition directly from TASK_FREEZABLE to TASK_FROZEN  are
> > always woken up on the thaw path. Prior to that commit, tasks could ask
> > freezer to consider them "frozen enough" via freezer_do_not_count(). The
> > commit replaced freezer_do_not_count() with a TASK_FREEZABLE state which
> > allows freezer to immediately mark the task as TASK_FROZEN without
> > waking up the task.  This is efficient for the suspend path, but on the
> > thaw path, the task is always woken up even if the task didn't need to
> > wake up and goes back to its TASK_(UN)INTERRUPTIBLE state. Although
> > these tasks are capable of handling of the wakeup, we can observe a
> > power/perf impact from the extra wakeup.
> 
> This issue is hurting the performance of our stable 6.1 releases. Does
> it make sense to backport these patches into stable branches once they
> land in mainline? I would assume we want to fix the perf regression
> there too?

Note that these patches are in tip/sched/core, slated for the next merge
window.