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

    > From: Suresh Siddha <suresh.b.siddha@intel.com>
    > Date: 2012/4/10
    > Subject: Re: [PATCH] clockevents: Leave broadcast device shtudown only
    > if the current device is always running.
    > To: Santosh Shilimkar <santosh.shilimkar@ti.com>
    > 抄送: tglx@linutronix.de, linux-kernel@vger.kernel.org, johnstul@us.ibm.com
    >
    >
    > On Mon, 2012-04-09 at 11:33 +0530, Santosh Shilimkar wrote:
    > > Commit 77b0d60{clockevents: Leave the broadcast device in shutdown mode
    > > when not needed} was intended to leave the broadcast device in shutdown mode
    > > when the per-cpu clockevent devices are always running.
    > >
    > > This breaks the systems where per cpu clock events stop in low power states.
    > >
    > > Hence revert 77b0d60 and implement the same requirement with use
    > > of C3STOP feature flag.
    >
    > Problem you encountered is not related to leaving the broadcast device
    > in shutdown mode. Problem is that we didn't track the mode change to
    > oneshot and later during idle entry/exit, when we request the broadcast
    > device services using CLOCK_EVT_NOTIFY_BROADCAST_ENTER etc,
    > tick_broadcast_oneshot_control() returns with out doing much as it
    > thinks broadcast device is in periodic mode.

    Just curious, IIUC, the tick_broadcast_switch_to_oneshot() is only called
    during CPU init process in boot time or bring a offlined cpu back on. Why
    is it related to the deep idle?

    Thanks,
    Feng
    >
    > Can you please check if the appended patch fixes the issue? I could
    > reproduce the issue on my NHM platform which doesn't have always running
    > apic timer and with the appended fix, all is well with cpu's going into
    > tickless idle etc. Thanks.
    > ---
    >
    > From: Suresh Siddha <suresh.b.siddha@intel.com>
    > Subject: clockevents: track broadcast device mode change in
    > tick_broadcast_switch_to_oneshot()
    >
    > In the commit 77b0d60c5adf39c74039e2142a1d3cd1e4d53799,
    > "clockevents: Leave the broadcast device in shutdown mode when not needed",
    > we were bailing out too quickly in tick_broadcast_switch_to_oneshot(),
    > with out tracking the broadcast device mode change to 'TICKDEV_MODE_ONESHOT'.
    >
    > This breaks the platforms which need broadcast device oneshot services during
    > deep idle states. tick_broadcast_oneshot_control() thinks that it is
    > in periodic mode and fails to take proper decisions based on the
    > CLOCK_EVT_NOTIFY_BROADCAST_[ENTER, EXIT] notifications during deep
    > idle entry/exit.
    >
    > Fix this by tracking the broadcast device mode as 'TICKDEV_MODE_ONESHOT',
    > before leaving the broadcast HW device in shutdown mode if there are no active
    > requests for the moment.
    >
    > Reported-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
    > Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
    > ---
    > kernel/time/tick-broadcast.c | 4 +++-
    > 1 files changed, 3 insertions(+), 1 deletions(-)
    >
    > diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
    > index e883f57..bf57abd 100644
    > --- a/kernel/time/tick-broadcast.c
    > +++ b/kernel/time/tick-broadcast.c
    > @@ -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);
    >
    >
    > --
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