linux-kernel - [PATCH v2 08/23] sched/cache: Calculate the per runqueue task LLC preference

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Message-Id: <f659bd08e561b377bb7057b6e1b5a656e738c8c6.1764801860.git.tim.c.chen@linux.intel.com>
Date: Wed,  3 Dec 2025 15:07:27 -0800
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>,
	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: [PATCH v2 08/23] sched/cache: Calculate the per runqueue task LLC preference

Calculate the number of tasks' LLC preferences for each runqueue.
This statistic is computed during task enqueue and dequeue
operations, and is used by the cache-aware load balancing.

Co-developed-by: Chen Yu <yu.c.chen@...el.com>
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
---

Notes:
    v1->v2: Split from previous patch for easier review.

 kernel/sched/fair.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d46a70a9d9fb..b0e87616e377 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1231,11 +1231,12 @@ static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
 		return;
 
 	pref_llc = p->preferred_llc;
-	if (pref_llc < 0)
+	if (pref_llc < 0 || pref_llc >= max_llcs)
 		return;
 
 	rq->nr_llc_running++;
 	rq->nr_pref_llc_running += (pref_llc == task_llc(p));
+	rq->nr_pref_llc[pref_llc]++;
 	p->sched_llc_active = true;
 }
 
@@ -1252,11 +1253,12 @@ static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
 		return;
 
 	pref_llc = p->preferred_llc;
-	if (pref_llc < 0)
+	if (pref_llc < 0 || pref_llc >= max_llcs)
 		return;
 
 	rq->nr_llc_running--;
 	rq->nr_pref_llc_running -= (pref_llc == task_llc(p));
+	rq->nr_pref_llc[pref_llc]--;
 	p->sched_llc_active = false;
 }
 
-- 
2.32.0