Messages in this thread | | | Subject | Re: [PATCH] clockevents: Leave broadcast device shtudown only if the current device is always running. | From | Suresh Siddha <> | Date | Mon, 16 Apr 2012 15:03:36 -0700 |
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On Sun, 2012-04-15 at 18:27 +0530, Santosh Shilimkar wrote: > On Tuesday 10 April 2012 04:11 AM, Suresh Siddha wrote: > > @@ -575,10 +575,12 @@ void tick_broadcast_switch_to_oneshot(void) > > unsigned long flags; > > > > raw_spin_lock_irqsave(&tick_broadcast_lock, flags); > > + > > + tick_broadcast_device.mode = TICKDEV_MODE_ONESHOT; > > + > > if (cpumask_empty(tick_get_broadcast_mask())) > > goto end; > > > > - tick_broadcast_device.mode = TICKDEV_MODE_ONESHOT; > > bc = tick_broadcast_device.evtdev; > > if (bc) > > tick_broadcast_setup_oneshot(bc); > > > > > Last time when I tried your patch, some how he ethernet IRQ masked > the issue. > > The problem is still as before. If you make a minimal kernel > configuration and possibly have only local timer, broadcast timer > and say console device as CPU wakeup sources, you should hang in > the boot process itself(Assuming CPUIDLE driver is built-in) > > The main issue is, you are not letting the one time setup > needed for the broadcast device. Even with above change, > the 'tick_broadcast_device.evtdev' is still in SHUTDOWN > mode and the event handler is pointing to clockevents_handle_noop()
On x86, idle driver (like drivers/idle/intel_idle.c: __setup_broadcast_timer()) calls clockevents_notify() with CLOCK_EVT_NOTIFY_BROADCAST_ON, during which we do tick_broadcast_setup_oneshot(). See tick_do_broadcast_on_off() which does this. That should setup the evtdev handler, mode etc.
And during the next CLOCK_EVT_NOTIFY_BROADCAST_ENTER we program the next broadcast event.
> So the very first 'CLOCK_EVT_NOTIFY_BROADCAST_ENTER' call won't > program the broadcast device with next event and CPU won't wakeup > from low power. if you are lucky and have some other wakeup source, > system will move further and eventually the handler and > mode of the broad-cast device get set correctly.
I am confused. Can you elaborate on how on the next spurious wakeup event, broad-cast device handler, mode is set?
It sounds like the CLOCK_EVT_NOTIFY_BROADCAST_ON/OFF notifications are missing from your idle driver. But I am confused how it will work on the next spurious wakeup etc with out the calls to tick_do_broadcast_on_off()? Perhaps the next spurious wakeup correcting everything is just theory and you didn't see it in practice?
Anyways, can you add CLOCK_EVT_NOTIFY_BROADCAST_ON/OFF notifications in your idle driver to see if it addresses the problem. That is the correct thing to do here.
thanks, suresh
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