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

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Date:   Wed, 24 Feb 2021 18:46:23 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, linux-kernel@...r.kernel.org,
        joel@...lfernandes.org
Cc:     fweisbec@...il.com, tglx@...utronix.de, qais.yousef@....com,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH 0/7 v4] move update blocked load outside newidle_balance

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


Otherwise, feel free to add to the lot:

  Reviewed-by: Valentin Schneider <valentin.schneider@....com>