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

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Message-ID: <a0456690-1917-4d82-877a-f23d871049b5@quicinc.com>
Date:   Thu, 28 Sep 2023 09:24:55 -0700
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     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

Hi Peter,

On 9/26/2023 1:02 PM, Peter Zijlstra wrote:
> 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.

Can the changes be scheduled for the next 6.6-rc? I'd like to get the
changes backported to stable sooner since we observed the regression on
real systems.

Thanks,
Elliot