We did not restart the tick device from irq_enter() to avoid double
reprogramming and extra events in the return immediate to idle case.
But long lasting softirqs can lead to a situation where jiffies become
stale:
idle()
tick stopped (reprogrammed to next pending timer)
halt()
interrupt
jiffies updated from irq_enter()
interrupt handler
softirq function 1 runs 20ms
softirq function 2 arms a 10ms timer with a stale jiffies value
jiffies updated from irq_exit()
timer wheel has now an already expired timer
(the one added in function 2)
timer fires and timer softirq runs
This was discovered when debugging a timer problem which happend only
when the ath5k driver is active. The debugging proved that there is a
softirq function running for more than 20ms, which is a bug by itself.
To solve this we restart the tick timer right from irq_enter(), but do
not go through the other functions which are necessary to return from
idle when need_resched() is set.
Reported-by: Elias Oltmanns <eo@nebensachen.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Elias Oltmanns <eo@nebensachen.de>
+/*
+ * Called from irq_enter() when idle was interrupted to reenable the
+ * per cpu device.
+ */
+void tick_check_oneshot_broadcast(int cpu)
+{
+ if (cpu_isset(cpu, tick_broadcast_oneshot_mask)) {
+ struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
+
+ clockevents_set_mode(td->evtdev, CLOCK_EVT_MODE_ONESHOT);
+ }
+}
+
/*
* Handle oneshot mode broadcasting
*/
/*
* Handle oneshot mode broadcasting
*/
extern void tick_shutdown_broadcast_oneshot(unsigned int *cpup);
extern int tick_resume_broadcast_oneshot(struct clock_event_device *bc);
extern int tick_broadcast_oneshot_active(void);
extern void tick_shutdown_broadcast_oneshot(unsigned int *cpup);
extern int tick_resume_broadcast_oneshot(struct clock_event_device *bc);
extern int tick_broadcast_oneshot_active(void);
+extern void tick_check_oneshot_broadcast(int cpu);
# else /* BROADCAST */
static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
{
# else /* BROADCAST */
static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
{
static inline void tick_broadcast_switch_to_oneshot(void) { }
static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
static inline int tick_broadcast_oneshot_active(void) { return 0; }
static inline void tick_broadcast_switch_to_oneshot(void) { }
static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
static inline int tick_broadcast_oneshot_active(void) { return 0; }
+static inline void tick_check_oneshot_broadcast(int cpu) { }
# endif /* !BROADCAST */
#else /* !ONESHOT */
# endif /* !BROADCAST */
#else /* !ONESHOT */
update_process_times(user_mode(regs));
profile_tick(CPU_PROFILING);
update_process_times(user_mode(regs));
profile_tick(CPU_PROFILING);
- /* Do not restart, when we are in the idle loop */
- if (ts->tick_stopped)
- return;
-
while (tick_nohz_reprogram(ts, now)) {
now = ktime_get();
tick_do_update_jiffies64(now);
while (tick_nohz_reprogram(ts, now)) {
now = ktime_get();
tick_do_update_jiffies64(now);
+/*
+ * When NOHZ is enabled and the tick is stopped, we need to kick the
+ * tick timer from irq_enter() so that the jiffies update is kept
+ * alive during long running softirqs. That's ugly as hell, but
+ * correctness is key even if we need to fix the offending softirq in
+ * the first place.
+ *
+ * Note, this is different to tick_nohz_restart. We just kick the
+ * timer and do not touch the other magic bits which need to be done
+ * when idle is left.
+ */
+static void tick_nohz_kick_tick(int cpu)
+{
+ struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+
+ if (!ts->tick_stopped)
+ return;
+
+ tick_nohz_restart(ts, ktime_get());
+}
+
#else
static inline void tick_nohz_switch_to_nohz(void) { }
#else
static inline void tick_nohz_switch_to_nohz(void) { }
*/
void tick_check_idle(int cpu)
{
*/
void tick_check_idle(int cpu)
{
+ tick_check_oneshot_broadcast(cpu);
#ifdef CONFIG_NO_HZ
tick_nohz_stop_idle(cpu);
tick_nohz_update_jiffies();
#ifdef CONFIG_NO_HZ
tick_nohz_stop_idle(cpu);
tick_nohz_update_jiffies();
+ tick_nohz_kick_tick(cpu);
profile_tick(CPU_PROFILING);
}
profile_tick(CPU_PROFILING);
}
- /* Do not restart, when we are in the idle loop */
- if (ts->tick_stopped)
- return HRTIMER_NORESTART;
-
hrtimer_forward(timer, now, tick_period);
return HRTIMER_RESTART;
hrtimer_forward(timer, now, tick_period);
return HRTIMER_RESTART;