[PATCH 10/12] hrtimer: Update hrtimer_resolution only if value changes

[Paul E. McKenney]

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>
Cc: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@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 53c57d585696..91ac2b517637 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 */
-- 
2.40.1