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

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Date:   Tue, 26 Sep 2023 16:17:33 +0000
From:   Carlos Llamas <cmllamas@...gle.com>
To:     Elliot Berman <quic_eberman@...cinc.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "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 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?

--
Carlos Llamas