On 03/27/2015 10:44 PM, Viresh Kumar wrote:
> Clockevent device can now be stopped by switching to ONESHOT_STOPPED state, to
> avoid getting spurious interrupts on a tickless CPU.
>
> Switch state to ONESHOT_STOPPED at following places:
>
> 1.) NOHZ_MODE_LOWRES Mode
>
> Timers & hrtimers are dependent on tick for their working in this mode and the
> only place from where clockevent device is programmed is the tick-code.
>
> In LOWRES mode we skip reprogramming the clockevent device in
> tick_nohz_stop_sched_tick() if expires == KTIME_MAX. In addition to that we
> must
> also switch the clockevent device to ONESHOT_STOPPED state to avoid all
> spurious
> interrupts that may follow.
>
> 2.) NOHZ_MODE_HIGHRES Mode
>
> Tick & timers are dependent on hrtimers for their working in this mode and the
> only place from where clockevent device is programmed is the hrtimer-code.
>
> There are two places here from which we reprogram the clockevent device or
> skip
> reprogramming it on expires == KTIME_MAX.
>
> Signed-off-by: Viresh Kumar <viresh.ku...@linaro.org>
> ---
> kernel/time/hrtimer.c | 46 ++++++++++++++++++++++++++++++++++++++++++----
> kernel/time/tick-sched.c | 3 +++
> 2 files changed, 45 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index 045ba7e2be6c..89d4b593dfc0 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -543,8 +543,19 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base
> *cpu_base, int skip_equal)
> if (cpu_base->hang_detected)
> return;
>
> - if (cpu_base->expires_next.tv64 != KTIME_MAX)
> + if (cpu_base->expires_next.tv64 != KTIME_MAX) {
> tick_program_event(cpu_base->expires_next, 1);
> + } else {
> + struct clock_event_device *dev =
> + __this_cpu_read(tick_cpu_device.evtdev);
> + /*
> + * Don't need clockevent device anymore, stop it.
> + *
> + * We reach here only for NOHZ_MODE_HIGHRES mode and we are
> + * guaranteed that no timers/hrtimers are enqueued on this cpu.
> + */
> + clockevents_set_state(dev, CLOCK_EVT_STATE_ONESHOT_STOPPED);
> + }
> }
>
> /*
> @@ -1312,9 +1323,36 @@ void hrtimer_interrupt(struct clock_event_device *dev)
> cpu_base->in_hrtirq = 0;
> raw_spin_unlock(&cpu_base->lock);
>
> - /* Reprogramming necessary ? */
> - if (expires_next.tv64 == KTIME_MAX ||
> - !tick_program_event(expires_next, 0)) {
> + if (expires_next.tv64 == KTIME_MAX) {
> + struct clock_event_device *dev =
> + __this_cpu_read(tick_cpu_device.evtdev);
> +
> + cpu_base->hang_detected = 0;
> +
> + /*
> + * Don't need clockevent device anymore, stop it.
> + *
> + * We reach here only for NOHZ_MODE_HIGHRES mode and we are
> + * guaranteed that no timers/hrtimers are enqueued on this cpu.
> + *
> + * Most of the scenarios will be covered by similar code
> + * present in hrtimer_force_reprogram(), as we always try to
> + * evaluate tick requirement on idle/irq exit and cancel
> + * tick-sched hrtimer when tick isn't required anymore.
> + *
> + * It is required here as well as a special case.
> + *
> + * Last hrtimer fires on a tickless CPU and doesn't rearm
> + * itself. tick_nohz_irq_exit() reevaluates next event and it
> + * gets expires == KTIME_MAX. Because tick was already stopped,
> + * and last expires == new_expires, we return early. And the
> + * clockevent device is never stopped.
> + */
> + clockevents_set_state(dev, CLOCK_EVT_STATE_ONESHOT_STOPPED);
> + return;
> + }
> +
> + if (!tick_program_event(expires_next, 0)) {
> cpu_base->hang_detected = 0;
> return;
> }
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 47c04edd07df..ff271a26fa4d 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -685,6 +685,9 @@ static ktime_t tick_nohz_stop_sched_tick(struct
> tick_sched *ts,
> if (unlikely(expires.tv64 == KTIME_MAX)) {
> if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
> hrtimer_cancel(&ts->sched_timer);
> + else
> + /* stop clock event device */
> + clockevents_set_state(dev,
> CLOCK_EVT_STATE_ONESHOT_STOPPED);
> goto out;
> }
>
Reviewed-by: Preeti U. Murthy <pre...@linux.vnet.ibm.com>
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