On Wed, Jan 20, 2016 at 07:26:14PM +0900, Byungchul Park wrote: > On Wed, Jan 20, 2016 at 02:43:35PM +0900, Byungchul Park wrote: > > > > It looks very tricky. I have a question. Do we have to call the > > scheduler_tick() even while the tick is stopped? IMHO, it seems to be > > ok even if we won't call it while the tick is stopped. Wrong? I mean, > > > > The reason why I asked is that, scheduler_tick() looks to be a > scheduler callback for *periodic tick*. IMHO, we need to choose one of > these two. > > 1) Make scheduler_tick() can handle it, not only for the periodic tick > but also for the tick-like event during tick-stopped. But I am not sure > if this is the right way. > > 2) Distinguish the periodic tick from the tick-like event by which we > can handle rcu callback, irq work and so on, so that the periodic tick > handler only handles periodic stuff either locally or remotely, while > the tick-like event handler only does its purpose. I think this is > better, I am sure though.
So lets check all the things we call on scheduler_tick(): _ sched_clock_tick(): maybe it doesn't need to be called when idle. I'm not sure. Some code in idle (timers, irqs, ...) might need to call sched_clock(). _ update_rq_clock(), task_tick(): task_tick is empty for idle class, so we probably don't need an updated rq either. _ update_cpu_load_active(): I was about to fix the issue properly and make it account correctly on idle ticks but we might as well want to spare it. _ calc_global_load_tick(): no idea _ perf_event_task_tick(): needed, some freq CPU events can trigger in idle and need adjustments _ trigger_load_balance(): maybe needed, I see it triggers the softirq after some rebalance delay, regardless of the current CPU idleness. _ rq_last_tick_reset(): not needed in idle Here we are. > > > --- > > > > diff --git a/kernel/time/timer.c b/kernel/time/timer.c > > index bbc5d11..774adc2 100644 > > --- a/kernel/time/timer.c > > +++ b/kernel/time/timer.c > > @@ -1422,7 +1422,8 @@ void update_process_times(int user_tick) > > if (in_irq()) > > irq_work_tick(); > > #endif > > - scheduler_tick(); > > + if (!tick_nohz_tick_stopped()) > > + scheduler_tick(); > > run_posix_cpu_timers(p); > > } > > > > --- > > > > hm ???
