[tip: timers/core] hrtimer: Update hrtimer_resolution only if value changes

[tip-bot2 for Paul E. McKenney]

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

Commit-ID:     15f84398330ce1c0aa3e1e3edd0c915324bed26b
Gitweb:        https://git.kernel.org/tip/15f84398330ce1c0aa3e1e3edd0c915324bed26b
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Fri, 18 Sep 2026 17:14:26 -07:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxx>
CommitterDate: Tue, 29 Sep 2026 21:02:52 +02:00

hrtimer: Update hrtimer_resolution only if value changes

Currently, the hrtimer_switch_to_hres() function unconditionally updates
hrtimer_resolution to HIGH_RES_NSEC.  This causes KCSAN false positives
in kernels built with CONFIG_KCSAN_STRICT=y.  It also causes unnecessary
cache-line traffic on the many code paths that load hrtimer_resolution,
which is especially regrettable because the value of hrtimer_resolution
normally changes only once during the lifetime of a given kernel.

Therefore, update the value of hrtimer_resolution to HIGH_RES_NSEC only
if it does not already have that value.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Link: https://patch.msgid.link/20260919001428.3133388-10-paulmck@xxxxxxxxxx
---
 kernel/time/hrtimer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 7b44a35..2054064 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -780,7 +780,8 @@ static void hrtimer_switch_to_hres(void)
 		return;
 	}
 	base->hres_active = true;
-	hrtimer_resolution = HIGH_RES_NSEC;
+	if (hrtimer_resolution != HIGH_RES_NSEC)
+		hrtimer_resolution = HIGH_RES_NSEC;
 
 	tick_setup_sched_timer(true);
 	/* "Retrigger" the interrupt to get things going */