linux-kernel - [RFC PATCH 14/19] sched/fair: Convert find_new_ilb() to use nohz_shared

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Message-ID: <20250904041516.3046-15-kprateek.nayak@amd.com>
Date: Thu, 4 Sep 2025 04:15:10 +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>, <linux-kernel@...r.kernel.org>
CC: 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>
Subject: [RFC PATCH 14/19] sched/fair: Convert find_new_ilb() to use nohz_shared_list

Use "nohz_shared_list" in find_new_ilb() instead of the global
"nohz.idle_cpus_mask".

Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
 kernel/sched/fair.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ad6e97be97d5..5e7198078d19 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12263,18 +12263,27 @@ static inline int on_null_domain(struct rq *rq)
  */
 static inline int find_new_ilb(void)
 {
+	struct sched_domain_shared *sds;
 	const struct cpumask *hk_mask;
-	int ilb_cpu;
 
 	hk_mask = housekeeping_cpumask(HK_TYPE_KERNEL_NOISE);
 
-	for_each_cpu_and(ilb_cpu, nohz.idle_cpus_mask, hk_mask) {
+	guard(rcu)();
+
+	list_for_each_entry_rcu(sds, &nohz_shared_list, nohz_list_node) {
+		int ilb_cpu;
 
-		if (ilb_cpu == smp_processor_id())
+		/* No idle CPUs in this domain */
+		if (!atomic_read(&sds->nr_idle_cpus))
 			continue;
 
-		if (idle_cpu(ilb_cpu))
-			return ilb_cpu;
+		for_each_cpu_and(ilb_cpu, sds->idle_cpus_mask, hk_mask) {
+			if (ilb_cpu == smp_processor_id())
+				continue;
+
+			if (idle_cpu(ilb_cpu))
+				return ilb_cpu;
+		}
 	}
 
 	return -1;
-- 
2.34.1