Re: [tip:sched/hrtick] [hrtimer] 2889243848: stress-ng.timermix.ops_per_sec 30.1% regression

[Peter Zijlstra]

On Tue, Mar 10, 2026 at 07:50:06PM +0100, Peter Zijlstra wrote:
> On Tue, Mar 10, 2026 at 07:16:51PM +0100, Peter Zijlstra wrote:
> > On Tue, Mar 10, 2026 at 01:11:09PM -0400, Joe Talbott wrote:
> > 
> > > It looks like it can be found here:
> > > https://download.01.org/0day-ci/archive/20260310/202603102229.74b9dee4-lkp@xxxxxxxxx/repro-script
> > > 
> > > stress-ng --timeout 60 --times --verify --metrics --no-rand-seed --timermix 64
> > 
> > Thanks, that does indeed work and show the regression.
> > 
> > Lets see if I can spot the fail...
> 
> It looks like that benchmark manages to trip significant nr_hangs, and
> yes, I made those more expensive because those were not expected to
> actually happen at any sane rate.
> 
> Lets see if we can cure that without making a giant mess of things.

Ha! This seems to work just fine.

---
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index b94bd56b739f..9872dd53f761 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -2031,7 +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);
+		expires_next = ktime_add_ns(ktime_get(),
+					    min(100 * NSEC_PER_MSEC, cpu_base->max_hang_time));
 		cpu_base->hang_detected = false;
 	}
 	hrtimer_rearm_event(expires_next, deferred);