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hrtimer: Less agressive interrupt 'hang' handling

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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 2889243848 ("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
 2889243848:   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: 2889243848 ("hrtimer: Re-arrange hrtimer_interrupt()")
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260311121500.GF652779@noisy.programming.kicks-ass.net
Closes: https://lore.kernel.org/oe-lkp/202603102229.74b9dee4-lkp@intel.com
This commit is contained in:
Peter Zijlstra
2026-03-10 20:02:21 +01:00
committed by Thomas Gleixner
parent eef9f648fb
commit 92f7ee408c
1 changed files with 3 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
kernel/time/hrtimer.c
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@@ -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 @@ void hrtimer_interrupt(struct clock_event_device *dev)
*/
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;