linux-kernel - Re: [PATCH v2 4/6] cgroup/cpuset: Iterate only if DEADLINE tasks are present

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Date:   Wed, 3 May 2023 13:56:34 -0400
From:   Waiman Long <longman@...hat.com>
To:     Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Qais Yousef <qyousef@...alina.io>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hao Luo <haoluo@...gle.com>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org,
        cgroups@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Wei Wang <wvw@...gle.com>, Rick Yiu <rickyiu@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v2 4/6] cgroup/cpuset: Iterate only if DEADLINE tasks are
 present

On 5/3/23 03:22, Juri Lelli wrote:
> update_tasks_root_domain currently iterates over all tasks even if no
> DEADLINE task is present on the cpuset/root domain for which bandwidth
> accounting is being rebuilt. This has been reported to introduce 10+ ms
> delays on suspend-resume operations.
>
> Skip the costly iteration for cpusets that don't contain DEADLINE tasks.
>
> Reported-by: Qais Yousef <qyousef@...alina.io>
> Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
> Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
> ---
>   kernel/cgroup/cpuset.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index b9f4d5602517..6587df42cb61 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1090,6 +1090,9 @@ static void dl_update_tasks_root_domain(struct cpuset *cs)
>   	struct css_task_iter it;
>   	struct task_struct *task;
>   
> +	if (cs->nr_deadline_tasks == 0)
> +		return;
> +
>   	css_task_iter_start(&cs->css, 0, &it);
>   
>   	while ((task = css_task_iter_next(&it)))
Reviewed-by: Waiman Long <longman@...hat.com>