linux-kernel - [RFC PATCH 12/08] sched/fair: Record the cpu that updated the stats last

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Message-ID: <20250316102916.10614-4-kprateek.nayak@amd.com>
Date: Sun, 16 Mar 2025 10:29:13 +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>, Chen Yu <yu.c.chen@...el.com>,
	<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>, David Vernet
	<void@...ifault.com>, "Gautham R. Shenoy" <gautham.shenoy@....com>, "Swapnil
 Sapkal" <swapnil.sapkal@....com>, Shrikanth Hegde <sshegde@...ux.ibm.com>, "K
 Prateek Nayak" <kprateek.nayak@....com>
Subject: [RFC PATCH 12/08] sched/fair: Record the cpu that updated the stats last

Record which CPU updated the stats last. This will be used to invalidate
the stats in the following commits.

Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
 kernel/sched/fair.c  | 5 +++--
 kernel/sched/sched.h | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6c486e194a9d..2a34d73d824b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10279,9 +10279,9 @@ static inline void cache_sd_stats(struct lb_env *env, struct sg_lb_stats *sd_sta
 {
 	struct sched_domain_shared *sd_share = env->sd->shared;
 	struct sg_lb_stats_prop *lb_prop;
-	int cpu, retry_limit = 3;
 	u64 time, lock;
 	long version;
+	int cpu;
 
 	if (!sd_share)
 		return;
@@ -10319,7 +10319,7 @@ static inline void cache_sd_stats(struct lb_env *env, struct sg_lb_stats *sd_sta
 		 * Version is up for grabs! Try again. If the CPU grabs
 		 * the lock next time around lock = version = 0 and this
 		 * is skipped. If it cannot grab the version, lock != 0
-		 * and we return from here thus ensuring on a single
+		 * and we return from here thus ensuring only a single
 		 * retry.
 		 */
 		if (!lock) {
@@ -10330,6 +10330,7 @@ static inline void cache_sd_stats(struct lb_env *env, struct sg_lb_stats *sd_sta
 	}
 
 	lb_prop->sg_stats = *sd_stats;
+	lb_prop->update_cpu = cpu;
 
 	/*
 	 * Pairs against readers checking the version
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 64f7e013fd59..adf4fa2ed031 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2197,6 +2197,7 @@ struct sg_lb_stats_prop {
 	 */
 	atomic_long_t		version;
 	struct sg_lb_stats	sg_stats;	/* Cached sched_group stats */
+	int			update_cpu;	/* CPU that updated the stats */
 };
 
 static inline struct cpumask *sched_group_span(struct sched_group *sg)
-- 
2.43.0