From: Peter Zijlstra Date: Tue, 10 Mar 2026 19:02:21 +0000 (+0100) Subject: hrtimer: Less agressive interrupt 'hang' handling X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=92f7ee408c23fcc074e4952fb6ffacdf3eb86b56;p=thirdparty%2Fkernel%2Flinux.git hrtimer: Less agressive interrupt 'hang' handling When the hrtimer_interrupt needs to restart more than 3 times and still has expired timers, the interrupt is considered hung. To give the system a little time to recover, the hardware timer is programmed a little into the future. Prior to commit 288924384856 ("hrtimer: Re-arrange hrtimer_interrupt()"), this was relative to the amount of time spend serving the interrupt with a max of 100 msec. However, in order to simplify, and because this condition 'should' not happen, the timeout was unconditionally set to 100 msec. 'Obviously' there is a benchmark that hits this hard, by programming a ton of very short timers :-/ Since reprogramming is decoupled from the interrupt handling, the actual execution time is lost, however the code does track max_hang_time. Using that, rather than the 100 ms max restores performance. stress-ng --timeout 60 --times --verify --metrics --no-rand-seed --timermix 64 bogo ops/s 288924384856^1: 23715979.93 288924384856: 11550049.77 patched: 23361116.78 Additionally, Thomas noted that cpu_base->hang_detected should not be cleared until the next interrupt, such that __hrtimer_reprogram() won't undo the extra delay. Fixes: 288924384856 ("hrtimer: Re-arrange hrtimer_interrupt()") Reported-by: kernel test robot Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Link: https://patch.msgid.link/20260311121500.GF652779@noisy.programming.kicks-ass.net Closes: https://lore.kernel.org/oe-lkp/202603102229.74b9dee4-lkp@intel.com --- diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index b94bd56b739f6..cafd6771a2255 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -2031,8 +2031,8 @@ static void hrtimer_rearm(struct hrtimer_cpu_base *cpu_base, ktime_t expires_nex * Give the system a chance to do something else than looping * on hrtimer interrupts. */ - expires_next = ktime_add_ns(ktime_get(), 100 * NSEC_PER_MSEC); - cpu_base->hang_detected = false; + expires_next = ktime_add_ns(ktime_get(), + min(100 * NSEC_PER_MSEC, cpu_base->max_hang_time)); } hrtimer_rearm_event(expires_next, deferred); } @@ -2121,6 +2121,7 @@ retry: */ now = hrtimer_update_base(cpu_base); expires_next = hrtimer_update_next_event(cpu_base); + cpu_base->hang_detected = false; if (expires_next < now) { if (++retries < 3) goto retry;