linux-kernel - Re: [PATCH v2] freezer,sched: Use saved_state to reduce some spurious wakeups

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Message-ID: <20230904212324.GA2568@noisy.programming.kicks-ass.net>
Date:   Mon, 4 Sep 2023 23:23:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Elliot Berman <quic_eberman@...cinc.com>
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 v2] freezer,sched: Use saved_state to reduce some
 spurious wakeups

On Wed, Aug 30, 2023 at 10:42:39AM -0700, Elliot Berman wrote:

> Avoid the spurious wakeups by saving the state of TASK_FREEZABLE tasks.
> If the task was running before entering TASK_FROZEN state
> (__refrigerator()) or if the task received a wake up for the saved
> state, then the task is woken on thaw. saved_state from PREEMPT_RT locks
> can be re-used because freezer would not stomp on the rtlock wait flow:
> TASK_RTLOCK_WAIT isn't considered freezable.

You don't actually assert that anywhere I think, so the moment someone
makes that happen you crash and burn.

Also:

> -#ifdef CONFIG_PREEMPT_RT
> +#if IS_ENABLED(CONFIG_PREEMPT_RT) || IS_ENABLED(CONFIG_FREEZER)

That makes wakeup more horrible for everyone :/