linux-kernel - Re: [PATCH 0/7 v4] move update blocked load outside newidle

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Date:   Thu, 25 Feb 2021 09:05:11 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Qais Yousef <qais.yousef@....com>
Subject: Re: [PATCH 0/7 v4] move update blocked load outside newidle_balance

Hi Valentin,

On Wed, 24 Feb 2021 at 19:46, Valentin Schneider
<valentin.schneider@....com> wrote:
>
> On 24/02/21 14:30, Vincent Guittot wrote:
> > Joel reported long preempt and irq off sequence in newidle_balance because
> > of a large number of CPU cgroups in use and having to be updated. This
> > patchset moves the update outside newidle_imblance. This enables to early
> > abort during the updates in case of pending irq as an example.
> >
> > Instead of kicking a normal ILB that will wakes up CPU which is already
> > idle, patch 6 triggers the update of statistics in the idle thread of
> > the CPU before selecting and entering an idle state.
> >
> > Changes on v4:
> > - Add a dedicated bit for updating blocked load when entering idle.
> >   This simplifies the management of concurrency with kick_ilb.
> >
>
> I believe that solves the issues vs nohz balance.
>
> One last thing for patch 7: mayhaps we could do a tad better to avoid
> duplicate updates going through a heapful of leaf cfs rqs, see
>
>   http://lore.kernel.org/r/jhj4kiht7oh.mognet@arm.com

rq->last_blocked_load_update_tick is there only to filter duplicate
update during _nohz_idle_balance but not for other normal LB.

>
>
> Otherwise, feel free to add to the lot:
>
>   Reviewed-by: Valentin Schneider <valentin.schneider@....com>
>