linux-kernel - Re: [PATCH v2 06/23] sched/cache: Track LLC-preferred tasks per runqueue

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Message-ID: <20251209121617.GN3707891@noisy.programming.kicks-ass.net>
Date: Tue, 9 Dec 2025 13:16:17 +0100
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>, Vern Hao <haoxing990@...il.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>,
	Adam Li <adamli@...amperecomputing.com>,
	Aaron Lu <ziqianlu@...edance.com>, Tim Chen <tim.c.chen@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/23] sched/cache: Track LLC-preferred tasks per
 runqueue

On Wed, Dec 03, 2025 at 03:07:25PM -0800, Tim Chen wrote:


>  #ifdef CONFIG_SCHED_CACHE
>  	struct callback_head		cache_work;
> +	/*the p is currently refcounted in a rq's preferred llc stats*/

Shall we have spaces after and before the comment marks?

Also, comment confuses me, I don't see get_task_struct() /
put_task_struct() usage. Did you mean something else with refcount?

> +	bool				sched_llc_active;
>  	int				preferred_llc;
>  #endif

> +static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
> +{
> +	int pref_llc;
> +
> +	/*
> +	 * Borrow the uc_se->active from uclamp_rq_inc_id(),
> +	 * uclamp_rq_dec_id() to avoid the unbalanced calculation
> +	 * of rq statistics.
> +	 */
> +	if (unlikely(!p->sched_llc_active))
> +		return;

Another very confusing comment; what? Also, can you please explain (in
the new comment) how we get here without having llc_active set?

> +
> +	pref_llc = p->preferred_llc;
> +	if (pref_llc < 0)
> +		return;
> +
> +	rq->nr_llc_running--;
> +	rq->nr_pref_llc_running -= (pref_llc == task_llc(p));
> +	p->sched_llc_active = false;
> +}