linux-kernel - Re: [PATCH v9 10/10] cpuidle: menu: Avoid selecting shallow states with stopped tick

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Date:   Thu, 5 Apr 2018 15:49:32 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Thomas Ilsche <thomas.ilsche@...dresden.de>,
        Doug Smythies <dsmythies@...us.net>,
        Rik van Riel <riel@...riel.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Mike Galbraith <mgalbraith@...e.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>
Subject: Re: [PATCH v9 10/10] cpuidle: menu: Avoid selecting shallow states
 with stopped tick

On Thu, Apr 5, 2018 at 2:47 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Apr 04, 2018 at 10:50:36AM +0200, Rafael J. Wysocki wrote:
>> +     if (tick_nohz_tick_stopped()) {
>> +             /*
>> +              * If the tick is already stopped, the cost of possible short
>> +              * idle duration misprediction is much higher, because the CPU
>> +              * may be stuck in a shallow idle state for a long time as a
>> +              * result of it.  In that case say we might mispredict and try
>> +              * to force the CPU into a state for which we would have stopped
>> +              * the tick, unless the tick timer is going to expire really
>> +              * soon anyway.
>
> Wait what; the tick was stopped, therefore it _cannot_ expire soon.
>
> *confused*
>
> Did you mean s/tick/a/ ?

Yeah, that should be "a timer".