linux-kernel - [tip: timers/core] timers/migration: Spare write when nothing changed

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Message-ID: <172011797324.2215.7387357188188957218.tip-bot2@tip-bot2>
Date: Thu, 04 Jul 2024 18:32:53 -0000
From: "tip-bot2 for Anna-Maria Behnsen" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Anna-Maria Behnsen" <anna-maria@...utronix.de>,
 Thomas Gleixner <tglx@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: timers/core] timers/migration: Spare write when nothing changed

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

Commit-ID:     2e0bd37f7b395173f879225b9d8b1811af4a8a35
Gitweb:        https://git.kernel.org/tip/2e0bd37f7b395173f879225b9d8b1811af4a8a35
Author:        Anna-Maria Behnsen <anna-maria@...utronix.de>
AuthorDate:    Mon, 01 Jul 2024 12:18:43 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 04 Jul 2024 20:24:57 +02:00

timers/migration: Spare write when nothing changed

The wakeup value is written unconditionally in tmigr_cpu_new_timer(). When
there was no new next timer expiry that needs to be propagated, then the
value that was read before is written. This is not required.

Move write to the place where wakeup value could have changed.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Link: https://lore.kernel.org/r/20240701-tmigr-fixes-v3-7-25cd5de318fb@linutronix.de

---
 kernel/time/timer_migration.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
index 9ff61f9..a2d156b 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -1215,14 +1215,13 @@ u64 tmigr_cpu_new_timer(u64 nextexp)
 		if (nextexp != tmc->cpuevt.nextevt.expires ||
 		    tmc->cpuevt.ignore) {
 			ret = tmigr_new_timer(tmc, nextexp);
+			/*
+			 * Make sure the reevaluation of timers in idle path
+			 * will not miss an event.
+			 */
+			WRITE_ONCE(tmc->wakeup, ret);
 		}
 	}
-	/*
-	 * Make sure the reevaluation of timers in idle path will not miss an
-	 * event.
-	 */
-	WRITE_ONCE(tmc->wakeup, ret);
-
 	trace_tmigr_cpu_new_timer_idle(tmc, nextexp);
 	raw_spin_unlock(&tmc->lock);
 	return ret;