On Thu, Mar 05, 2015 at 10:06:30AM +0530, Preeti U Murthy wrote:
>
> On 03/02/2015 08:23 PM, Peter Zijlstra wrote:
> > On Thu, Feb 26, 2015 at 08:52:02AM +0530, Preeti U Murthy wrote:
> >> The hrtimer mode of broadcast queues hrtimers in the idle entry
> >> path so as to wakeup cpus in deep idle states.
> >
> > Callgraph please...
>
> cpuidle_idle_call()
> |____ clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, ....))
> |_____tick_broadcast_set_event()
> |____clockevents_program_event()
> |____bc_set_next()
> >
> >> hrtimer_{start/cancel}
> >> functions call into tracing which uses RCU. But it is not legal to call
> >> into RCU in cpuidle because it is one of the quiescent states. Hence
> >> protect this region with RCU_NONIDLE which informs RCU that the cpu
> >> is momentarily non-idle.
> >
> > It it not clear to me that every user of bc_set_next() is from IDLE.
> > From what I can tell it ends up being clockevents_program_event() and
> > that is called quite a lot.
>
> bc_set_next() is called from at places:
> 1. Idle entry : It is called when a cpu in its idle entry path finds the
> need to reset the broadcast hrtimer.
> 2. CPU offline operations : When the cpu on which the broadcast hrtimer
> is being queued goes offline.
>
> So you see that almost all the time, it is called in idle entry path.
How about:
hrtimer_reprogram()
tick_program_event()
clockevents_program_event()
->set_next_ktime()
That is called from !idle loads of times. I guess I'm not seeing what
avoids &ce_broadcast_hrtimer from being the 'normal' clock event.
Sure; it might be that for power you only end up with that broadcast
crap enabled on idle/hotplug, but is this always so?
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