On Fri, Apr 11, 2014 at 04:53:35PM +0200, Frederic Weisbecker wrote: > On Fri, Apr 11, 2014 at 03:34:23PM +0530, Viresh Kumar wrote: > > On 10 April 2014 20:09, Frederic Weisbecker <[email protected]> wrote: > > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > > > index 9f8af69..1e2d6b7 100644 > > > --- a/kernel/time/tick-sched.c > > > +++ b/kernel/time/tick-sched.c > > > @@ -202,13 +202,16 @@ static void tick_nohz_restart_sched_tick(struct > > > tick_sched *ts, ktime_t now); > > > void __tick_nohz_full_check(void) > > > { > > > struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); > > > + unsigned long flags; > > > > > > + local_irq_save(flags); > > > > As we need to disable interrupts to read this variable, would it be > > better to just remove this completely and use is_idle_task(current) > > instead? > > I don't get what you mean. The goal was get read of the hammer is_idle_task() > check, wasn't it? > > Also irqs are disabled but this is fundamentaly not required as this can only > be > called by IPIs which always have irqs disabled. > > Hmm I should add a WARN_ON_(!irqs_disabled()) though just in case. > > > > > > if (tick_nohz_full_cpu(smp_processor_id())) { > > > - if (ts->tick_stopped && !is_idle_task(current)) { > > > + if (ts->tick_stopped && !ts->inidle)) { > > > if (!can_stop_full_tick()) > > > tick_nohz_restart_sched_tick(ts, > > > ktime_get()); > > > } > > > } > > > + local_irq_restore(flags); > > > } > > > > > If you like it I'll push it to Ingo. > > > > Yes please. And thanks for the explanations. It was pretty useful. > > > > I am looking to offload 1 second tick to timekeeping CPUs and so > > going through these frameworks. I don't have a working solution yet > > (even partially :)). Would send a RFC to you as soon as I get anything > > working. > > I see. The only solution I can think of right now is to have the timekeeper > call > sched_class(current[$CPU])::scheduler_tick() on behalf of all full dynticks > CPUs. > > This sounds costly but can be done once per sec for each CPUs. Not sure if > Peterz will > like it but sending mockup RFC patches will tell us more about his opinion :)
I think there's assumptions that tick runs on the local cpu; also what are you going to do when running it on all remote cpus takes longer than the tick? > Otherwise (and ideally) we need to make the scheduler code able to handle > long periods without > calling scheduler_tick(). But this is a lot more plumbing. And the scheduler > has gazillions > accounting stuffs to handle. Sounds like a big nightmare to take that > direction. So i'm not at all sure what you guys are talking about, but it seems to me you should all put down the bong and have a detox round instead. This all sounds like a cure worse than the problem. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
