linux-kernel - Re: [PATCH 07/19] sched/fair: Track LLC-preferred tasks per runqueue

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Message-ID: <fe5eeffc-ff8f-4bfb-b0a1-5b25731afb88@amd.com>
Date: Mon, 27 Oct 2025 11:34:58 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Tim Chen <tim.c.chen@...ux.intel.com>, Peter Zijlstra
	<peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, "Gautham R . Shenoy"
	<gautham.shenoy@....com>
CC: Vincent Guittot <vincent.guittot@...aro.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>, Valentin Schneider <vschneid@...hat.com>, "Madadi Vineeth
 Reddy" <vineethr@...ux.ibm.com>, Hillf Danton <hdanton@...a.com>, "Shrikanth
 Hegde" <sshegde@...ux.ibm.com>, Jianyong Wu <jianyong.wu@...look.com>, Yangyu
 Chen <cyy@...self.name>, Tingyin Duan <tingyin.duan@...il.com>, "Vern Hao"
	<vernhao@...cent.com>, Len Brown <len.brown@...el.com>, Aubrey Li
	<aubrey.li@...el.com>, Zhao Liu <zhao1.liu@...el.com>, Chen Yu
	<yu.chen.surf@...il.com>, Chen Yu <yu.c.chen@...el.com>, Libo Chen
	<libo.chen@...cle.com>, Adam Li <adamli@...amperecomputing.com>, Tim Chen
	<tim.c.chen@...el.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/19] sched/fair: Track LLC-preferred tasks per runqueue

Hello Tim,

On 10/11/2025 11:54 PM, Tim Chen wrote:
> @@ -3999,6 +4038,7 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  		struct rq *rq = rq_of(cfs_rq);
>  
>  		account_numa_enqueue(rq, task_of(se));
> +		account_llc_enqueue(rq, task_of(se));
>  		list_add(&se->group_node, &rq->cfs_tasks);
>  	}
>  	cfs_rq->nr_queued++;
> @@ -4010,9 +4050,14 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  	update_load_sub(&cfs_rq->load, se->load.weight);
>  	if (entity_is_task(se)) {
>  		account_numa_dequeue(rq_of(cfs_rq), task_of(se));
> +		account_llc_dequeue(rq_of(cfs_rq), task_of(se));
>  		list_del_init(&se->group_node);
>  	}
>  	cfs_rq->nr_queued--;
> +
> +	/* safeguard to clear the cache aware data */
> +	if (!parent_entity(se) && !cfs_rq->nr_queued)
> +		reset_llc_stats(rq_of(cfs_rq));

Instead of relying on reset_llc_stats() hack, I think a better approach
would be to have a "p->se.llc_sched_active" flag similar to how uclamp
has "uc_se->active" and we set this in account_llc_enqueue() which will
still check for sched_cache_enabled() but account_llc_dequeue() would
only check for "p->se.llc_sched_active" to decrement the stats and then
unset the flag.

That way, we cannot have an imbalanced accounting. Thoughts?

>  }
>  

-- 
Thanks and Regards,
Prateek