linux-kernel - Re: [PATCH v2] sched/freq: move call to cpufreq_update

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Message-ID: <bcba52bc-6780-1efc-6ef4-1a75f1cef33d@arm.com>
Date:   Wed, 13 Nov 2019 15:09:47 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mel Gorman <mgorman@...e.de>,
        Doug Smythies <dsmythies@...us.net>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sargun Dhillon <sargun@...gun.me>, Tejun Heo <tj@...nel.org>,
        Xie XiuQi <xiexiuqi@...wei.com>, xiezhipeng1@...wei.com,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v2] sched/freq: move call to cpufreq_update_util

On 13.11.19 14:30, Vincent Guittot wrote:
> On Wed, 13 Nov 2019 at 11:50, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>>
>> On 12.11.19 16:05, Vincent Guittot wrote:
>>> Le Tuesday 12 Nov 2019 à 15:48:13 (+0100), Vincent Guittot a écrit :

[...]

>>>> @@ -7493,9 +7495,9 @@ static void update_blocked_averages(int cpu)
>>>>       * that RT, DL and IRQ signals have been updated before updating CFS.
>>>>       */
>>>>      curr_class = rq->curr->sched_class;
>>>> -    update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
>>>> -    update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
>>>> -    update_irq_load_avg(rq, 0);
>>>> +    decayed |= update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
>>>> +    decayed |= update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
>>>> +    decayed |= update_irq_load_avg(rq, 0);
>>
>> Why not 'decayed  = update_cfs_rq_load_avg()' like in the
>> !CONFIG_FAIR_GROUP_SCHED case?
> 
> Because it is handled by the update_load_avg() in
> for_each_leaf_cfs_rq_safe() loop
> 
> This means that we can have 2 calls to cpufreq_update_util in
> update_blocked_average() but at least the values will be up to date in
> both calls unlike previously.
> 
> I'm going to prepare an additional patch to remove this useless call.
> I have also seen some possible further optimization that i need to
> study a bit more before preparing a patch

I see. The update_load_avg() call for the taskgroup skeleton se
(cfs_rq->tg->se[cpu]). But what happens to the cpu which only has the
root cfs_rq i the list? It doesn't have a skeleton se.