linux-kernel - Re: [RFC PATCH v2 1/7] sched/fair: Add related data structure for task based throttle

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Message-ID: <a227dd46-e6ec-4cc3-a0a3-427c4ffc9d07@amd.com>
Date: Mon, 14 Apr 2025 09:28:36 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Aaron Lu <ziqianlu@...edance.com>, Valentin Schneider
	<vschneid@...hat.com>, Ben Segall <bsegall@...gle.com>, Peter Zijlstra
	<peterz@...radead.org>, Josh Don <joshdon@...gle.com>, Ingo Molnar
	<mingo@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, Xi Wang
	<xii@...gle.com>
CC: <linux-kernel@...r.kernel.org>, Juri Lelli <juri.lelli@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt
	<rostedt@...dmis.org>, Mel Gorman <mgorman@...e.de>, Chengming Zhou
	<chengming.zhou@...ux.dev>, Chuyi Zhou <zhouchuyi@...edance.com>, Jan Kiszka
	<jan.kiszka@...mens.com>
Subject: Re: [RFC PATCH v2 1/7] sched/fair: Add related data structure for
 task based throttle

Hello Aaron,

On 4/9/2025 5:37 PM, Aaron Lu wrote:
> From: Valentin Schneider <vschneid@...hat.com>
> 
> Add related data structures for this new throttle functionality.
> 
> Signed-off-by: Valentin Schneider <vschneid@...hat.com>
> Signed-off-by: Aaron Lu <ziqianlu@...edance.com>
> ---
>   include/linux/sched.h |  4 ++++
>   kernel/sched/core.c   |  3 +++
>   kernel/sched/fair.c   | 12 ++++++++++++
>   kernel/sched/sched.h  |  2 ++
>   4 files changed, 21 insertions(+)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index f96ac19828934..0b55c79fee209 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -880,6 +880,10 @@ struct task_struct {
>   
>   #ifdef CONFIG_CGROUP_SCHED
>   	struct task_group		*sched_task_group;
> +#ifdef CONFIG_CFS_BANDWIDTH
> +	struct callback_head		sched_throttle_work;
> +	struct list_head		throttle_node;

Since throttled tasks are fully dequeued before placing on the
"throttled_limbo_list", is it possible to reuse "p->se.group_node"?

Currently, it is used to track the task on "rq->cfs_tasks" and during
load-balancing when moving a bunch of tasks between CPUs but since a
fully throttled task is not tracked by either, it should be safe to
reuse this bit (CONFIG_DEBUG_LIST will scream if I'm wrong) and save
up on some space in the  task_struct.

Thoughts?

-- 
Thanks and Regards,
Prateek

> +#endif
>   #endif
>