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    Subject[PATCH 4/4] Avoid broadcast time lock when not changing the timeout
    Date
    From: Andi Kleen <ak@linux.intel.com>

    Don't take the global lock when the new timeout is larger than the
    old timeout.

    The timeout on the broadcast device should never shrink, so this
    is safe to do.

    Signed-off-by: Andi Kleen <ak@linux.intel.com>
    ---
    kernel/time/tick-broadcast.c | 17 ++++++++++++-----
    1 files changed, 12 insertions(+), 5 deletions(-)

    diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
    index c1587cb..4776742 100644
    --- a/kernel/time/tick-broadcast.c
    +++ b/kernel/time/tick-broadcast.c
    @@ -524,6 +524,17 @@ static void set_broadcast_sibling_state(int cpu, int enter)
    }
    }

    +static void set_broadcast_timeout(ktime_t to, struct clock_event_device *bc)
    +{
    + unsigned long flags;
    +
    + if (to.tv64 < bc->next_event.tv64) {
    + raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
    + tick_broadcast_set_event(to, 1);
    + raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
    + }
    +}
    +
    /*
    * Powerstate information: The system enters/leaves a state, where
    * affected devices might stop
    @@ -532,7 +543,6 @@ void tick_broadcast_oneshot_control(unsigned long reason)
    {
    struct clock_event_device *bc, *dev;
    struct tick_device *td;
    - unsigned long flags;
    int cpu;
    ktime_t timeout;

    @@ -556,14 +566,12 @@ void tick_broadcast_oneshot_control(unsigned long reason)
    reason == CLOCK_EVT_NOTIFY_BROADCAST_ENTER))
    return;

    - raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
    if (reason == CLOCK_EVT_NOTIFY_BROADCAST_ENTER) {
    if (!__get_cpu_var(state).need_oneshot) {
    /* Turn all slaves into oneshots */
    set_broadcast_sibling_state(cpu, 1);
    clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN);
    - if (timeout.tv64 < bc->next_event.tv64)
    - tick_broadcast_set_event(timeout, 1);
    + set_broadcast_timeout(timeout, bc);
    }
    } else {
    if (__get_cpu_var(state).need_oneshot) {
    @@ -574,7 +582,6 @@ void tick_broadcast_oneshot_control(unsigned long reason)
    tick_program_event(dev->next_event, 1);
    }
    }
    - raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
    }

    /*
    --
    1.7.4.4


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