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    SubjectRe: [PATCH] clockevents: Leave broadcast device shtudown only if the current device is always running.
    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.


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      Last update: 2012-04-17 00:03    [W:0.031 / U:15.284 seconds]
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