linux-kernel - [PATCH 6/6] sched/fair: reduce the window for duplicated update

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Date:   Fri,  5 Feb 2021 12:48:30 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, fweisbec@...il.com, tglx@...utronix.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org,
        joel@...lfernandes.org
Cc:     qais.yousef@....com, Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 6/6] sched/fair: reduce the window for duplicated update

Start to update last_blocked_load_update_tick to reduce the possibility
of another cpu starting the update one more time

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3d2ab28d5736..968808c2c022 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7852,17 +7852,9 @@ static inline bool others_have_blocked(struct rq *rq)
 	return false;
 }
 
-static inline void update_blocked_load_status(struct rq *rq, bool has_blocked)
-{
-	rq->last_blocked_load_update_tick = jiffies;
-
-	if (!has_blocked)
-		rq->has_blocked_load = 0;
-}
 #else
 static inline bool cfs_rq_has_blocked(struct cfs_rq *cfs_rq) { return false; }
 static inline bool others_have_blocked(struct rq *rq) { return false; }
-static inline void update_blocked_load_status(struct rq *rq, bool has_blocked) {}
 #endif
 
 static bool __update_blocked_others(struct rq *rq, bool *done)
@@ -8022,12 +8014,16 @@ static void update_blocked_averages(int cpu)
 	struct rq_flags rf;
 
 	rq_lock_irqsave(rq, &rf);
+	WRITE_ONCE(rq->last_blocked_load_update_tick, jiffies);
+
 	update_rq_clock(rq);
 
 	decayed |= __update_blocked_others(rq, &done);
 	decayed |= __update_blocked_fair(rq, &done);
 
-	update_blocked_load_status(rq, !done);
+	if (done)
+		rq->has_blocked_load = 0;
+
 	if (decayed)
 		cpufreq_update_util(rq, 0);
 	rq_unlock_irqrestore(rq, &rf);
@@ -8363,7 +8359,7 @@ static bool update_nohz_stats(struct rq *rq)
 	if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
 		return false;
 
-	if (!time_after(jiffies, rq->last_blocked_load_update_tick))
+	if (!time_after(jiffies, READ_ONCE(rq->last_blocked_load_update_tick)))
 		return true;
 
 	update_blocked_averages(cpu);
-- 
2.17.1