[patch 03/12] hrtimer: Use hrtimer_start_expires_user() for hrtimer sleepers

Thomas Gleixner
2026-04-07T08:54:31Z

Most hrtimer sleepers are user controlled and user space can hand arbitrary
expiry values in as long as they are valid timespecs. If the expiry value
is in the past then this requires a full loop through reprogramming the
clock event device, taking the hrtimer interrupt, waking the task and
reprogram again.

Use hrtimer_start_expires_user() which avoids the full round trip by
checking the timer for expiry on enqueue.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
---
kernel/time/hrtimer.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -2152,7 +2152,11 @@ void hrtimer_sleeper_start_expires(struc
if (IS_ENABLED(CONFIG_PREEMPT_RT) && sl->timer.is_hard)
mode |= HRTIMER_MODE_HARD;

- hrtimer_start_expires(&sl->timer, mode);
+ /* If already expired, clear the task pointer and set current state to running */
+ if (!hrtimer_start_expires_user(&sl->timer, mode)) {
+ sl->task = NULL;
+ __set_current_state(TASK_RUNNING);
+ }
}
EXPORT_SYMBOL_GPL(hrtimer_sleeper_start_expires);