| Message ID | 20201223092034.528782-2-ramesh.thomas@intel.com |
|---|---|
| State | New |
| Headers | show |
| Series | [1/1] dynticks/preempt_rt: Fix a nohz_full entry failure in preempt_rt | expand |
On 2020-12-23 04:20:36 [-0500], ramesh.thomas@intel.com wrote: > From: Ramesh Thomas <ramesh.thomas@intel.com> > > After all conditions to enter nohz_full state are met, if a timer event > is detected in the next period, nohz_full entry is aborted in > tick_nohz_next_event(). In the failure condition, this scenario keeps > repeating. This has been reproduced in preempt_rt kernel, however it may > not be limited to it. Which timer is? Why does it make sense to enter NOHZ_FULL if the timer expires shortly after (in next jiffy window if I understood it properly). > Not bailing out if CONFIG_NO_HZ_FULL is defined, fixes the issue. Since > in NO_HZ_FULL mode, idle state is not entered at tick stoppage, the > pending timer event can be handled where the next timer is programmed in > tick_nohz_stop_tick(). This also simplifies the logic by keeping a > common path to handle the entry/exit of nohz_full state, whether the > tick was already stopped or not. > > (The entire check for the presence of a timer event in the next period > can possibly be skipped for NO_HZ_FULL) > > Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com> > --- > kernel/time/tick-sched.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 308a98c28ee8..3798dbc5f082 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -739,10 +739,12 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) > * We've not stopped the tick yet, and there's a timer in the > * next period, so no point in stopping it either, bail. > */ > +#ifndef CONFIG_NO_HZ_FULL > if (!ts->tick_stopped) { > ts->timer_expires = 0; > - goto out; > + return 0; > } > +#endif > } > > /* > @@ -763,7 +765,6 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) > > ts->timer_expires = min_t(u64, expires, next_tick); > > -out: > return ts->timer_expires; > } > > -- > 2.26.2 > Sebastian
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 308a98c28ee8..3798dbc5f082 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -739,10 +739,12 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) * We've not stopped the tick yet, and there's a timer in the * next period, so no point in stopping it either, bail. */ +#ifndef CONFIG_NO_HZ_FULL if (!ts->tick_stopped) { ts->timer_expires = 0; - goto out; + return 0; } +#endif } /* @@ -763,7 +765,6 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) ts->timer_expires = min_t(u64, expires, next_tick); -out: return ts->timer_expires; }