linux-kernel - [RESEND RFC PATCH v2 05/29] sched/fair: Simplity SIS_UTIL handling in select_idle

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251208092744.32737-5-kprateek.nayak@amd.com>
Date: Mon, 8 Dec 2025 09:26:51 +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 05/29] sched/fair: Simplity SIS_UTIL handling in select_idle_cpu()

Use the "sd_llc" passed to select_idle_cpu() to obtain the
"sd_llc_shared" instead of dereferencing the per-CPU variable.
While at it move the cpumask_and() operation after the SIS_UTIL bailout
check to avoid unnecessarily computing the cpumask.

Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
 kernel/sched/fair.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6e1c78142536..20198aa64882 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7636,21 +7636,18 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 {
 	struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask);
 	int i, cpu, idle_cpu = -1, nr = INT_MAX;
-	struct sched_domain_shared *sd_share;
-
-	cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
 
 	if (sched_feat(SIS_UTIL)) {
-		sd_share = rcu_dereference(per_cpu(sd_llc_shared, target));
-		if (sd_share) {
-			/* because !--nr is the condition to stop scan */
-			nr = READ_ONCE(sd_share->nr_idle_scan) + 1;
-			/* overloaded LLC is unlikely to have idle cpu/core */
-			if (nr == 1)
-				return -1;
-		}
+		/* because !--nr is the condition to stop scan */
+		nr = READ_ONCE(sd->shared->nr_idle_scan) + 1;
+		/* overloaded LLC is unlikely to have idle cpu/core */
+		if (nr == 1)
+			return -1;
 	}
 
+	if (!cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr))
+		return -1;
+
 	if (static_branch_unlikely(&sched_cluster_active)) {
 		struct sched_group *sg = sd->groups;
 
-- 
2.43.0