linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Valentin Schneider <valentin.schneider@arm.com>
To: Vincent Donnefort <vincent.donnefort@arm.com>,
	peterz@infradead.org, mingo@redhat.com,
	vincent.guittot@linaro.org
Cc: linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com,
	morten.rasmussen@arm.com, qperret@google.com,
	Vincent Donnefort <vincent.donnefort@arm.com>
Subject: Re: [PATCH 3/3] sched/fair: Do not raise overutilized for idle CPUs
Date: Mon, 20 Dec 2021 17:17:38 +0000	[thread overview]
Message-ID: <8735mn8abx.mognet@arm.com> (raw)
In-Reply-To: <20211220114323.22811-4-vincent.donnefort@arm.com>

On 20/12/21 12:43, Vincent Donnefort wrote:
> During a migration, the lock for the previous runqueue is not taken and
> hence, the task contribution isn't directly removed from that runqueue
> utilization but instead temporarily saved, until the next PELT signals
> update where it would be accounted. There is then a window in which a
> CPU can ben idle be nonetheless overutilized.
>
> The load balancer wouldn't be able to do anything to help a sleeping CPU,
> it brings then no gain to raise overutilized there, only the risk of
> spuriously doing it.
>
> Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>
>

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

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 51f6f55abb37..37f737c5f0b8 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8641,26 +8641,28 @@ static inline void update_sg_lb_stats(struct lb_env *env,
>
>               nr_running = rq->nr_running;
>               sgs->sum_nr_running += nr_running;
> -
> -		if (nr_running > 1)
> -			*sg_status |= SG_OVERLOAD;
> -
> -		if (cpu_overutilized(i))
> -			*sg_status |= SG_OVERUTILIZED;
> -
>  #ifdef CONFIG_NUMA_BALANCING
>               sgs->nr_numa_running += rq->nr_numa_running;
>               sgs->nr_preferred_running += rq->nr_preferred_running;
>  #endif
> +		if (nr_running > 1)
> +			*sg_status |= SG_OVERLOAD;
> +
>               /*
>                * No need to call idle_cpu() if nr_running is not 0
>                */
>               if (!nr_running && idle_cpu(i)) {
>                       sgs->idle_cpus++;
> -			/* Idle cpu can't have misfit task */
> +			/*
> +			 * Idle cpu can neither be overutilized nor have a
> +			 * misfit task.
> +			 */
>                       continue;
>               }
>
> +		if (cpu_overutilized(i))
> +			*sg_status |= SG_OVERUTILIZED;
> +
>               if (local_group)
>                       continue;
>
> --
> 2.25.1

  reply	other threads:[~2021-12-20 17:17 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-20 11:43 [PATCH 0/3] Fix stuck overutilized Vincent Donnefort
2021-12-20 11:43 ` [PATCH 1/3] sched/fair: Make cpu_overutilized() EAS dependent Vincent Donnefort
2021-12-20 17:17   ` Valentin Schneider
2021-12-21  9:09     ` Vincent Donnefort
2021-12-20 11:43 ` [PATCH 2/3] sched/fair: Fix newidle_balance() for overutilized systems Vincent Donnefort
2021-12-20 17:17   ` Valentin Schneider
2021-12-22  8:14   ` Vincent Guittot
2022-01-10 16:29     ` Vincent Donnefort
2021-12-20 11:43 ` [PATCH 3/3] sched/fair: Do not raise overutilized for idle CPUs Vincent Donnefort
2021-12-20 17:17   ` Valentin Schneider [this message]
2021-12-22  8:20   ` Vincent Guittot
2022-01-10 16:40     ` Vincent Donnefort
2022-01-17 10:45       ` Vincent Guittot
2022-01-17 12:18         ` Vincent Donnefort

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=8735mn8abx.mognet@arm.com \
    --to=valentin.schneider@arm.com \
    --cc=dietmar.eggemann@arm.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=morten.rasmussen@arm.com \
    --cc=peterz@infradead.org \
    --cc=qperret@google.com \
    --cc=vincent.donnefort@arm.com \
    --cc=vincent.guittot@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).