[tip: sched/hrtick] sched/fair: Simplify hrtick_update()

[tip-bot2 for Peter Zijlstra (Intel)]

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

Commit-ID:     97015376642f3cb7aa5c3cdb13bf094e94fbcd81
Gitweb:        https://git.kernel.org/tip/97015376642f3cb7aa5c3cdb13bf094e94fbcd81
Author:        Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
AuthorDate:    Tue, 24 Feb 2026 17:35:22 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 27 Feb 2026 16:40:03 +01:00

sched/fair: Simplify hrtick_update()

hrtick_update() was needed when the slice depended on nr_running, all that
code is gone. All that remains is starting the hrtick when nr_running
becomes more than 1.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260224163428.866374835@xxxxxxxxxx
---
 kernel/sched/fair.c  | 12 ++++--------
 kernel/sched/sched.h |  4 ++++
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 247fecd..0b6ce88 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6769,9 +6769,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 }
 
 /*
- * called from enqueue/dequeue and updates the hrtick when the
- * current task is from our class and nr_running is low enough
- * to matter.
+ * Called on enqueue to start the hrtick when h_nr_queued becomes more than 1.
  */
 static void hrtick_update(struct rq *rq)
 {
@@ -6780,6 +6778,9 @@ static void hrtick_update(struct rq *rq)
 	if (!hrtick_enabled_fair(rq) || donor->sched_class != &fair_sched_class)
 		return;
 
+	if (hrtick_active(rq))
+		return;
+
 	hrtick_start_fair(rq, donor);
 }
 #else /* !CONFIG_SCHED_HRTICK: */
@@ -7102,9 +7103,6 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
 		WARN_ON_ONCE(!task_sleep);
 		WARN_ON_ONCE(p->on_rq != 1);
 
-		/* Fix-up what dequeue_task_fair() skipped */
-		hrtick_update(rq);
-
 		/*
 		 * Fix-up what block_task() skipped.
 		 *
@@ -7138,8 +7136,6 @@ static bool dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	/*
 	 * Must not reference @p after dequeue_entities(DEQUEUE_DELAYED).
 	 */
-
-	hrtick_update(rq);
 	return true;
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b82fb70..73bc20c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3041,6 +3041,10 @@ static inline int hrtick_enabled_dl(struct rq *rq)
 }
 
 extern void hrtick_start(struct rq *rq, u64 delay);
+static inline bool hrtick_active(struct rq *rq)
+{
+	return hrtimer_active(&rq->hrtick_timer);
+}
 
 #else /* !CONFIG_SCHED_HRTICK: */