linux-kernel - [RESEND RFC PATCH v2 04/29] sched/fair: Simplify the entry condition for update_idle_cpu

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Message-ID: <20251208092744.32737-4-kprateek.nayak@amd.com>
Date: Mon, 8 Dec 2025 09:26:50 +0000
From: K Prateek Nayak <kprateek.nayak@....com>
To: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
	<vincent.guittot@...aro.org>, Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>, Thomas Gleixner
	<tglx@...utronix.de>
CC: <linux-kernel@...r.kernel.org>, 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>, K Prateek Nayak <kprateek.nayak@....com>, "Gautham R.
 Shenoy" <gautham.shenoy@....com>, Swapnil Sapkal <swapnil.sapkal@....com>,
	Shrikanth Hegde <sshegde@...ux.ibm.com>, Chen Yu <yu.c.chen@...el.com>
Subject: [RESEND RFC PATCH v2 04/29] sched/fair: Simplify the entry condition for update_idle_cpu_scan()

Only the topmost SD_SHARE_LLC domain has the "sd->shared" assigned.
Simply use "sd->shared" as an indicator for load balancing at the highest
SD_SHARE_LLC domain in update_idle_cpu_scan() instead of relying on
llc_size.

Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
 kernel/sched/fair.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b135c9ce21fe..6e1c78142536 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11005,6 +11005,7 @@ static void update_idle_cpu_scan(struct lb_env *env,
 				 unsigned long sum_util)
 {
 	struct sched_domain_shared *sd_share;
+	struct sched_domain *sd = env->sd;
 	int llc_weight, pct;
 	u64 x, y, tmp;
 	/*
@@ -11018,11 +11019,7 @@ static void update_idle_cpu_scan(struct lb_env *env,
 	if (!sched_feat(SIS_UTIL) || env->idle == CPU_NEWLY_IDLE)
 		return;
 
-	llc_weight = per_cpu(sd_llc_size, env->dst_cpu);
-	if (env->sd->span_weight != llc_weight)
-		return;
-
-	sd_share = rcu_dereference(per_cpu(sd_llc_shared, env->dst_cpu));
+	sd_share = sd->shared;
 	if (!sd_share)
 		return;
 
@@ -11056,10 +11053,11 @@ static void update_idle_cpu_scan(struct lb_env *env,
 	 */
 	/* equation [3] */
 	x = sum_util;
+	llc_weight = sd->span_weight;
 	do_div(x, llc_weight);
 
 	/* equation [4] */
-	pct = env->sd->imbalance_pct;
+	pct = sd->imbalance_pct;
 	tmp = x * x * pct * pct;
 	do_div(tmp, 10000 * SCHED_CAPACITY_SCALE);
 	tmp = min_t(long, tmp, SCHED_CAPACITY_SCALE);
-- 
2.43.0