Re: [PATCH 16/20] sched/idle: Use explicit broadcast oneshot control function

[Sudeep Holla]

On 28/04/15 15:14, Rafael J. Wysocki wrote:
> On Tuesday, April 28, 2015 03:37:44 PM Rafael J. Wysocki wrote:
> > On Tuesday, April 28, 2015 03:31:54 PM Rafael J. Wysocki wrote:
> > > On Tuesday, April 28, 2015 02:37:10 PM Linus Walleij wrote:
> > > > On Tue, Apr 28, 2015 at 2:19 PM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> > > > > Sudeep:
> > > > > > At-least I observed issue only when I am using hardware broadcast timer.
> > > > > > It doesn't hang when I am using hrtimer as broadcast timer in which case
> > > > > > one of the cpu will be not enter deeper idle states that lose timer.
> > > > > > I will rerun on v4.1-rc1 and post the complete log.
> > > > >
> > > > > So the bug here is that cpuidle_enter() enables interrupts, so the
> > > > > assumption about them being not enabled made by
> > > > > tick_broadcast_oneshot_control() is actually not valid.
> > > > >
> > > > > It looks like we need to acquire the clockevents_lock at least in this
> > > > > particular case.  Let me see where to put it and I'll send a patch for
> > > > > testing.
> > > >
> > > > Aha that looks very much like it. Put me on the patch and I'll
> > > > take it for a spin.
> > >
> > > OK, so something like the below for starters (the _irqsave variant is used to
> > > avoid adding one more WARN_ON(irqs_disabled()) in there).
> > >
> > > I haven't tested it, but then I can't reproduce the original issue in the
> > > first place.
> >
> > Of course, the whole "broadcast" thing could be done from cpuidle_enter()
> > in the first place, but then we could not avoid the problem with the cpuidle
> > *callback* enabling interrupts possibly in there anyway (not to mention the
> > "coupled" stuff).
>
> That said, if the given state is marked with CPUIDLE_FLAG_TIMER_STOP, I really
> wouldn't expect it to re-enable interrupts on exit and the "coupled" thing
> seems to be fundamentally at odds with that flag either.
>
> So it should be possible to move the "broadcast" logic into the cpuidle layer,
> which I'm going to try to do.

Makes sense.

> Please test the patch I've sent, though, as it should bring the code back to
> where it was before the clockevents_notify() removal and it'd be good to verify
> that.

I tested your patch and it works now. Anyways I am continuing to run
stress tests on my board. I will report if I find any issues.

Regards,
Sudeep
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