linux-kernel - Re: [BUG] schedutil governor produces regular max freq spikes because of lockup detector watchdog threads

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Date:   Wed, 10 Jan 2018 09:38:29 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Leonard Crestez <leonard.crestez@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Anson Huang <anson.huang@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [BUG] schedutil governor produces regular max freq spikes
 because of lockup detector watchdog threads

On 09-01-18, 16:43, Leonard Crestez wrote:
> What I am saying is that as far as I can tell when cpufreq_update_util
> is called when the task has already executed and is been switched out.

Can you check if this patch makes it any better ?

https://marc.info/?l=linux-kernel&m=151204248901636&w=2

> My tests are not very elaborate but based on some ftracing it seems to
> me that the current behavior is for cpufreq spikes to always trail RT
> activity. Like this:
> 
>           <idle>-0     [002]   496.510138: sched_switch:         swapper/2:0 [120] S ==> watchdog/2:20 [0]
>       watchdog/2-20    [002]   496.510156: bprint:               watchdog: IN watchdog(2)
>       watchdog/2-20    [002]   496.510364: bprint:               watchdog: OU watchdog(2)
>       watchdog/2-20    [002]   496.510377: bprint:               update_curr_rt: watchdog kick RT! cpu=2 comm=watchdog/2

Probabl update_curr_rt is getting called a bit after the task has
already run. The above patch moves the call to cpufreq_update_util()
to enqueue/dequeue paths and that should fix it.

-- 
viresh