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;
}
--
2.3.0.rc0.44.ga94655d
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