On 03/27/2015 10:44 PM, Viresh Kumar wrote:
> Next commit would update clockevents core to switch clockevent devices to
> ONESHOT_STOPPED state to avoid getting spurious interrupts on a tickless CPU.
>
> Before programming the clockevent device for next event, we must switch its
> state to ONESHOT.
>
> Switch state back to ONESHOT from 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.
>
> Two routines can restart ticks in LOWRES mode: tick_nohz_restart() and
> tick_nohz_stop_sched_tick().
>
> 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.
>
> Only hrtimer_reprogram() is responsible for programming the clockevent device
> for next event, if the clockevent device is stopped earlier. And updating that
> alone is sufficient here.
>
> To make sure we haven't missed any corner case, add a WARN() for the case
> where
> we try to reprogram clockevent device while we aren't configured in
> ONESHOT_STOPPED state.
>
> Signed-off-by: Viresh Kumar <viresh.ku...@linaro.org>
> ---
> kernel/time/clockevents.c | 4 ++++
> kernel/time/hrtimer.c | 5 +++++
> kernel/time/tick-sched.c | 14 +++++++++++++-
> 3 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
> index 04f6c3433f8e..e95896fd21fd 100644
> --- a/kernel/time/clockevents.c
> +++ b/kernel/time/clockevents.c
> @@ -335,6 +335,10 @@ int clockevents_program_event(struct clock_event_device
> *dev, ktime_t expires,
> if (dev->state == CLOCK_EVT_STATE_SHUTDOWN)
> return 0;
>
> + /* We must be in ONESHOT state here */
> + WARN_ONCE(dev->state != CLOCK_EVT_STATE_ONESHOT, "Current state: %d\n",
> + dev->state);
> +
> /* Shortcut for clockevent devices that can deal with ktime. */
> if (dev->features & CLOCK_EVT_FEAT_KTIME)
> return dev->set_next_ktime(expires, dev);
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index bee0c1f78091..045ba7e2be6c 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -566,6 +566,7 @@ static int hrtimer_reprogram(struct hrtimer *timer,
> {
> struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
> ktime_t expires = ktime_sub(hrtimer_get_expires(timer), base->offset);
> + struct clock_event_device *dev =
> __this_cpu_read(tick_cpu_device.evtdev);
> int res;
>
> WARN_ON_ONCE(hrtimer_get_expires_tv64(timer) < 0);
> @@ -610,6 +611,10 @@ static int hrtimer_reprogram(struct hrtimer *timer,
> if (cpu_base->hang_detected)
> return 0;
>
> + /* Switchback to ONESHOT state */
> + if (unlikely(dev->state == CLOCK_EVT_STATE_ONESHOT_STOPPED))
> + clockevents_set_state(dev, CLOCK_EVT_STATE_ONESHOT);
> +
> /*
> * Clockevents returns -ETIME, when the event was in the past.
> */
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index a4c4edac4528..47c04edd07df 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -694,8 +694,14 @@ static ktime_t tick_nohz_stop_sched_tick(struct
> tick_sched *ts,
> /* Check, if the timer was already in the past */
> if (hrtimer_active(&ts->sched_timer))
> goto out;
> - } else if (!tick_program_event(expires, 0))
> + } else {
> + /* Switchback to ONESHOT state */
> + if (unlikely(dev->state ==
> CLOCK_EVT_STATE_ONESHOT_STOPPED))
> + clockevents_set_state(dev,
> CLOCK_EVT_STATE_ONESHOT);
> +
> + if (!tick_program_event(expires, 0))
> goto out;
> + }
> /*
> * We are past the event already. So we crossed a
> * jiffie boundary. Update jiffies and raise the
> @@ -873,6 +879,8 @@ ktime_t tick_nohz_get_sleep_length(void)
>
> static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
> {
> + struct clock_event_device *dev =
> __this_cpu_read(tick_cpu_device.evtdev);
> +
> hrtimer_cancel(&ts->sched_timer);
> hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
>
> @@ -887,6 +895,10 @@ static void tick_nohz_restart(struct tick_sched *ts,
> ktime_t now)
> if (hrtimer_active(&ts->sched_timer))
> break;
> } else {
> + /* Switchback to ONESHOT state */
> + if (likely(dev->state ==
> CLOCK_EVT_STATE_ONESHOT_STOPPED))
> + clockevents_set_state(dev,
> CLOCK_EVT_STATE_ONESHOT);
> +
> if (!tick_program_event(
> hrtimer_get_expires(&ts->sched_timer), 0))
> break;
>
Reviewed-by: Preeti U. Murthy <pre...@linux.vnet.ibm.com>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
