Re: [RFC PATCH] tick/sched: update full_nohz status after SCHED dep is cleared

[Juri Lelli]

On 20/05/20 19:02, Frederic Weisbecker wrote:
> On Wed, May 20, 2020 at 06:49:25PM +0200, Juri Lelli wrote:
> > On 20/05/20 18:24, Frederic Weisbecker wrote:
> > 
> > Hummm, so I enabled 'timer:*', anything else you think I should be
> > looking at?
> 
> Are you sure you also enabled timer_expire_entry?
> Because:

I run with

trace-cmd record -e sched_switch -e sched_wakeup -e sched_migrate_task \
-e 'timer:*' -e 'irq_vectors:*' -e 'irq:softirq*' \
-e 'irq:irq_handler*' taskset --cpu-list 4-35 ./sysjitter/sysjitter \
--runtime 10 200

And

$ grep ' timer_expire_entry:' trace.txt | wc -l
1173

seems to confirm that the event was indeed enabled, e.g.

ksoftirqd/11-100   [011]   159.270023: timer_expire_entry:   timer=0xffff9807df8a5a60 function=delayed_work_timer_fn now=4294826418 baseclk=4294825984

> 
> > 
> > ...
> > ksoftirqd/13-117   [013]   148.265945: softirq_entry:        vec=1 [action=TIMER]
> 
> ...the timer softirq keep triggering without any timer callback executed. If that's the
> case, we may be dealing with an interesting issue.
> 
> Thanks.
> 
> > ksoftirqd/13-117   [013]   148.265947: softirq_exit:         vec=1 [action=TIMER]
> > ksoftirqd/13-117   [013]   148.265948: softirq_entry:        vec=7 [action=SCHED]
> > ksoftirqd/13-117   [013]   148.265950: softirq_exit:         vec=7 [action=SCHED]
> > ksoftirqd/13-117   [013]   148.265952: sched_switch:         ksoftirqd/13:117 [120] S ==> sysjitter:2536 [120]
> >    sysjitter-2536  [013]   148.266912: local_timer_entry:    vector=236
> >    sysjitter-2536  [013]   148.266914: hrtimer_cancel:       hrtimer=0xffff9807df91bee0
> >    sysjitter-2536  [013]   148.266916: hrtimer_expire_entry: hrtimer=0xffff9807df91bee0 now=148249107837 function=tick_sched_timer/0x0
> >    sysjitter-2536  [013]   148.266918: softirq_raise:        vec=1 [action=TIMER]
> >    sysjitter-2536  [013]   148.266920: softirq_raise:        vec=7 [action=SCHED]
> >    sysjitter-2536  [013]   148.266922: hrtimer_expire_exit:  hrtimer=0xffff9807df91bee0
> >    sysjitter-2536  [013]   148.266924: hrtimer_start:        hrtimer=0xffff9807df91bee0 function=tick_sched_timer/0x0 expires=148250105422 softexpires=148250105422
> >    sysjitter-2536  [013]   148.266926: local_timer_exit:     vector=236
> >    sysjitter-2536  [013]   148.266930: sched_wakeup:         ksoftirqd/13:117 [120] success=1 CPU:013
> >    sysjitter-2536  [013]   148.266932: tick_stop:            success=0 dependency=SCHED
> >    sysjitter-2536  [013]   148.266934: irq_work_entry:       vector=246
> >    sysjitter-2536  [013]   148.266936: irq_work_exit:        vector=246
> >    sysjitter-2536  [013]   148.266937: tick_stop:            success=0 dependency=SCHED
> >    sysjitter-2536  [013]   148.266940: sched_switch:         sysjitter:2536 [120] R ==> ksoftirqd/13:117 [120]
> > ksoftirqd/13-117   [013]   148.266943: softirq_entry:        vec=1 [action=TIMER]
> > ksoftirqd/13-117   [013]   148.266946: softirq_exit:         vec=1 [action=TIMER]
> > ksoftirqd/13-117   [013]   148.266946: softirq_entry:        vec=7 [action=SCHED]
> > ksoftirqd/13-117   [013]   148.266948: softirq_exit:         vec=7 [action=SCHED]
> > ksoftirqd/13-117   [013]   148.266950: sched_switch:         ksoftirqd/13:117 [120] S ==> sysjitter:2536 [120]
> >    sysjitter-2536  [013]   148.267912: local_timer_entry:    vector=236
> >    sysjitter-2536  [013]   148.267914: hrtimer_cancel:       hrtimer=0xffff9807df91bee0
> >    sysjitter-2536  [013]   148.267916: hrtimer_expire_entry: hrtimer=0xffff9807df91bee0 now=148250107750 function=tick_sched_timer/0x0
> >    sysjitter-2536  [013]   148.267918: softirq_raise:        vec=1 [action=TIMER]
> >    sysjitter-2536  [013]   148.267920: softirq_raise:        vec=7 [action=SCHED]
> >    sysjitter-2536  [013]   148.267922: hrtimer_expire_exit:  hrtimer=0xffff9807df91bee0
> >    sysjitter-2536  [013]   148.267924: hrtimer_start:        hrtimer=0xffff9807df91bee0 function=tick_sched_timer/0x0 expires=148251105422 softexpires=148251105422
> >    sysjitter-2536  [013]   148.267926: local_timer_exit:     vector=236
> >    sysjitter-2536  [013]   148.267929: sched_wakeup:         ksoftirqd/13:117 [120] success=1 CPU:013
> >    sysjitter-2536  [013]   148.267931: tick_stop:            success=0 dependency=SCHED
> >    sysjitter-2536  [013]   148.267934: irq_work_entry:       vector=246
> >    sysjitter-2536  [013]   148.267936: irq_work_exit:        vector=246
> >    sysjitter-2536  [013]   148.267937: tick_stop:            success=0 dependency=SCHED
> >    sysjitter-2536  [013]   148.267940: sched_switch:         sysjitter:2536 [120] R ==> ksoftirqd/13:117 [120]
> > ksoftirqd/13-117   [013]   148.267943: softirq_entry:        vec=1 [action=TIMER]
> > ksoftirqd/13-117   [013]   148.267945: softirq_exit:         vec=1 [action=TIMER]
> > ksoftirqd/13-117   [013]   148.267946: softirq_entry:        vec=7 [action=SCHED]
> > ksoftirqd/13-117   [013]   148.267947: softirq_exit:         vec=7 [action=SCHED]
> > ksoftirqd/13-117   [013]   148.267949: sched_switch:         ksoftirqd/13:117 [120] S ==> sysjitter:2536 [120]
> >    sysjitter-2536  [013]   148.268865: call_function_single_entry: vector=251
> >    sysjitter-2536  [013]   148.268867: call_function_single_exit: vector=251
> >    sysjitter-2536  [013]   148.268870: tick_stop:            success=1 dependency=NONE
> >    sysjitter-2536  [013]   148.268872: hrtimer_cancel:       hrtimer=0xffff9807df91bee0
> >    sysjitter-2536  [013]   148.268876: call_function_single_entry: vector=251
> >    sysjitter-2536  [013]   148.268878: call_function_single_exit: vector=251
> > ...
> > 
> > it looks like tick sched timer is kept armed until tick_stop
> > succedes (because of the check performed after _single_exit)?
> > 
> > Thanks for your quick reply!
> > 
>