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

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Message-ID: <20251015120523.GT3289052@noisy.programming.kicks-ass.net>
Date: Wed, 15 Oct 2025 14:05:23 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	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

On Sat, Oct 11, 2025 at 11:24:44AM -0700, 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);

Here and...

>  	}
>  	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));

... here, could you please check the compiler is doing CSE of task_of()?

>  		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));

I'm confused -- why?