On Fri, Nov 18, 2011 at 03:47:10PM -0800, Jeff Ohlstein wrote:
> __remove_hrtimer() attempts to reprogram the clockevent device when
> the timer being removed is the next to expire. However,
> __remove_hrtimer() reprograms the clockevent *before* removing the
> timer from the timerqueue and thus when hrtimer_force_reprogram()
> finds the next timer to expire it finds the timer we're trying to
> remove.
>
> This is especially noticeable when the system switches to NOHz mode
> and the system tick is removed. The timer tick is removed from the
> system but the clockevent is programmed to wakeup in another HZ
> anyway.
Reduced one needless call of hrtimer_interrupt() indeed.
>
> Silence the extra wakeup by removing the timer from the timerqueue
> before calling hrtimer_force_reprogram() so that we actually program
> the clockevent for the next timer to expire.
>
> This was broken by 998adc3 "hrtimers: Convert hrtimers to use
> timerlist infrastructure".
The issue also exists before 998adc3.
Apart from that.
Reviewed-by: Yong Zhang <yong.zhang0@xxxxxxxxx>
>
> Signed-off-by: Jeff Ohlstein <johlstei@xxxxxxxxxxxxxx>
> ---
> kernel/hrtimer.c | 6 ++++--
> 1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index 422e567..ae34bf5 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -885,10 +885,13 @@ static void __remove_hrtimer(struct hrtimer *timer,
> struct hrtimer_clock_base *base,
> unsigned long newstate, int reprogram)
> {
> + struct timerqueue_node *next_timer;
> if (!(timer->state & HRTIMER_STATE_ENQUEUED))
> goto out;
>
> - if (&timer->node == timerqueue_getnext(&base->active)) {
> + next_timer = timerqueue_getnext(&base->active);
> + timerqueue_del(&base->active, &timer->node);
> + if (&timer->node == next_timer) {
> #ifdef CONFIG_HIGH_RES_TIMERS
> /* Reprogram the clock event device. if enabled */
> if (reprogram && hrtimer_hres_active()) {
> @@ -901,7 +904,6 @@ static void __remove_hrtimer(struct hrtimer *timer,
> }
> #endif
> }
> - timerqueue_del(&base->active, &timer->node);
> if (!timerqueue_getnext(&base->active))
> base->cpu_base->active_bases &= ~(1 << base->index);
> out:
> --
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
>
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