linux-kernel - Re: [RESEND PATCH v1 1/2] cpuidle: menu: Correct the criteria for stopping tick

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Date:   Mon, 13 Aug 2018 10:01:20 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [RESEND PATCH v1 1/2] cpuidle: menu: Correct the criteria for
 stopping tick

On Sun, Aug 12, 2018 at 6:07 PM <leo.yan@...aro.org> wrote:
>
> On Sun, Aug 12, 2018 at 01:12:41PM +0200, Rafael J. Wysocki wrote:
> > On Fri, Aug 10, 2018 at 11:03 AM <leo.yan@...aro.org> wrote:

[cut]

> >
> > Assuming shot noise wakeups, if
> > drv->states[drv->state_count-1].target_residency is less than
> > TICK_USEC, the tick will be stopped for CPUs more often on average
> > with the patch applied (simply because the idle duration range for
> > which it will not be stopped is narrower then).
>
> Yes, good point, so in the new approach I try to change the code
> to compare with next tick delta rather than TICK_USEC, it can keeps
> running tick for the tick with long expire time (similiar with
> comparing with TICK_USEC) but we also can stop tick if the tick is likely
> to break idle residency.

We tried something similar and the results were not encouraging.
Please see https://lore.kernel.org/lkml/079e16b6-2e04-2518-0553-66becab226a6@tu-dresden.de/