[tip: sched/core] sched/fair: Reduce the window for duplicated update

["tip-bot2 for Vincent Guittot" <tip-bot2@xxxxxxxxxxxxx>]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     780eec5b50930b34e2f096b4dce5368d90497b55
Gitweb:        https://git.kernel.org/tip/780eec5b50930b34e2f096b4dce5368d90497b55
Author:        Vincent Guittot <vincent.guittot@xxxxxxxxxx>
AuthorDate:    Wed, 24 Feb 2021 14:30:07 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 03 Mar 2021 10:32:59 +01:00

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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Link: https://lkml.kernel.org/r/20210224133007.28644-8-vincent.guittot@xxxxxxxxxx
---
 kernel/sched/fair.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e87e1b3..f1b55f9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7852,16 +7852,20 @@ static inline bool others_have_blocked(struct rq *rq)
 	return false;
 }
 
-static inline void update_blocked_load_status(struct rq *rq, bool has_blocked)
+static inline void update_blocked_load_tick(struct rq *rq)
 {
-	rq->last_blocked_load_update_tick = jiffies;
+	WRITE_ONCE(rq->last_blocked_load_update_tick, jiffies);
+}
 
+static inline void update_blocked_load_status(struct rq *rq, bool has_blocked)
+{
 	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_tick(struct rq *rq) {}
 static inline void update_blocked_load_status(struct rq *rq, bool has_blocked) {}
 #endif
 
@@ -8022,6 +8026,7 @@ static void update_blocked_averages(int cpu)
 	struct rq_flags rf;
 
 	rq_lock_irqsave(rq, &rf);
+	update_blocked_load_tick(rq);
 	update_rq_clock(rq);
 
 	decayed |= __update_blocked_others(rq, &done);
@@ -8363,7 +8368,7 @@ 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);