* [PATCH] tick: Detect and fix jiffies update stall
@ 2022-02-02 0:01 Frederic Weisbecker
2022-02-02 1:49 ` Paul E. McKenney
0 siblings, 1 reply; 4+ messages in thread
From: Frederic Weisbecker @ 2022-02-02 0:01 UTC (permalink / raw)
To: Paul E . McKenney; +Cc: LKML, Frederic Weisbecker, Thomas Gleixner
On some rare cases, the timekeeper CPU may be delaying its jiffies
update duty for a while. Known causes include:
* The timekeeper is waiting on stop_machine in a MULTI_STOP_DISABLE_IRQ
or MULTI_STOP_RUN state. Disabled interrupts prevent from timekeeping
updates while waiting for the target CPU to complete its
stop_machine() callback.
* The timekeeper vcpu has VMEXIT'ed for a long while due to some overload
on the host.
Detect and fix these situations with emergency timekeeping catchups.
Original-patch-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/tick-sched.c | 17 +++++++++++++++++
kernel/time/tick-sched.h | 4 ++++
2 files changed, 21 insertions(+)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 17a283ce2b20..c89f50a7e690 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -169,6 +169,8 @@ static ktime_t tick_init_jiffy_update(void)
return period;
}
+#define MAX_STALLED_JIFFIES 5
+
static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
{
int cpu = smp_processor_id();
@@ -196,6 +198,21 @@ static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
if (tick_do_timer_cpu == cpu)
tick_do_update_jiffies64(now);
+ /*
+ * If jiffies update stalled for too long (timekeeper in stop_machine()
+ * or VMEXIT'ed for several msecs), force an update.
+ */
+ if (ts->last_tick_jiffies != jiffies) {
+ ts->stalled_jiffies = 0;
+ ts->last_tick_jiffies = READ_ONCE(jiffies);
+ } else {
+ if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) {
+ tick_do_update_jiffies64(now);
+ ts->stalled_jiffies = 0;
+ ts->last_tick_jiffies = READ_ONCE(jiffies);
+ }
+ }
+
if (ts->inidle)
ts->got_idle_tick = 1;
}
diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
index d952ae393423..504649513399 100644
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -49,6 +49,8 @@ enum tick_nohz_mode {
* @timer_expires_base: Base time clock monotonic for @timer_expires
* @next_timer: Expiry time of next expiring timer for debugging purpose only
* @tick_dep_mask: Tick dependency mask - is set, if someone needs the tick
+ * @last_tick_jiffies: Value of jiffies seen on last tick
+ * @stalled_jiffies: Number of stalled jiffies detected across ticks
*/
struct tick_sched {
struct hrtimer sched_timer;
@@ -77,6 +79,8 @@ struct tick_sched {
u64 next_timer;
ktime_t idle_expires;
atomic_t tick_dep_mask;
+ unsigned long last_tick_jiffies;
+ unsigned int stalled_jiffies;
};
extern struct tick_sched *tick_get_tick_sched(int cpu);
--
2.25.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] tick: Detect and fix jiffies update stall
2022-02-02 0:01 [PATCH] tick: Detect and fix jiffies update stall Frederic Weisbecker
@ 2022-02-02 1:49 ` Paul E. McKenney
2022-02-02 2:19 ` Frederic Weisbecker
0 siblings, 1 reply; 4+ messages in thread
From: Paul E. McKenney @ 2022-02-02 1:49 UTC (permalink / raw)
To: Frederic Weisbecker; +Cc: LKML, Thomas Gleixner
On Wed, Feb 02, 2022 at 01:01:07AM +0100, Frederic Weisbecker wrote:
> On some rare cases, the timekeeper CPU may be delaying its jiffies
> update duty for a while. Known causes include:
>
> * The timekeeper is waiting on stop_machine in a MULTI_STOP_DISABLE_IRQ
> or MULTI_STOP_RUN state. Disabled interrupts prevent from timekeeping
> updates while waiting for the target CPU to complete its
> stop_machine() callback.
>
> * The timekeeper vcpu has VMEXIT'ed for a long while due to some overload
> on the host.
>
> Detect and fix these situations with emergency timekeeping catchups.
>
> Original-patch-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
Nice, thank you!
So I should revert your earlier patch, apply this one, and then test
the result?
Thanx, Paul
> ---
> kernel/time/tick-sched.c | 17 +++++++++++++++++
> kernel/time/tick-sched.h | 4 ++++
> 2 files changed, 21 insertions(+)
>
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 17a283ce2b20..c89f50a7e690 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -169,6 +169,8 @@ static ktime_t tick_init_jiffy_update(void)
> return period;
> }
>
> +#define MAX_STALLED_JIFFIES 5
> +
> static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
> {
> int cpu = smp_processor_id();
> @@ -196,6 +198,21 @@ static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
> if (tick_do_timer_cpu == cpu)
> tick_do_update_jiffies64(now);
>
> + /*
> + * If jiffies update stalled for too long (timekeeper in stop_machine()
> + * or VMEXIT'ed for several msecs), force an update.
> + */
> + if (ts->last_tick_jiffies != jiffies) {
> + ts->stalled_jiffies = 0;
> + ts->last_tick_jiffies = READ_ONCE(jiffies);
> + } else {
> + if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) {
> + tick_do_update_jiffies64(now);
> + ts->stalled_jiffies = 0;
> + ts->last_tick_jiffies = READ_ONCE(jiffies);
> + }
> + }
> +
> if (ts->inidle)
> ts->got_idle_tick = 1;
> }
> diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
> index d952ae393423..504649513399 100644
> --- a/kernel/time/tick-sched.h
> +++ b/kernel/time/tick-sched.h
> @@ -49,6 +49,8 @@ enum tick_nohz_mode {
> * @timer_expires_base: Base time clock monotonic for @timer_expires
> * @next_timer: Expiry time of next expiring timer for debugging purpose only
> * @tick_dep_mask: Tick dependency mask - is set, if someone needs the tick
> + * @last_tick_jiffies: Value of jiffies seen on last tick
> + * @stalled_jiffies: Number of stalled jiffies detected across ticks
> */
> struct tick_sched {
> struct hrtimer sched_timer;
> @@ -77,6 +79,8 @@ struct tick_sched {
> u64 next_timer;
> ktime_t idle_expires;
> atomic_t tick_dep_mask;
> + unsigned long last_tick_jiffies;
> + unsigned int stalled_jiffies;
> };
>
> extern struct tick_sched *tick_get_tick_sched(int cpu);
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] tick: Detect and fix jiffies update stall
2022-02-02 1:49 ` Paul E. McKenney
@ 2022-02-02 2:19 ` Frederic Weisbecker
2022-02-02 17:24 ` Paul E. McKenney
0 siblings, 1 reply; 4+ messages in thread
From: Frederic Weisbecker @ 2022-02-02 2:19 UTC (permalink / raw)
To: Paul E. McKenney; +Cc: LKML, Thomas Gleixner
On Tue, Feb 01, 2022 at 05:49:34PM -0800, Paul E. McKenney wrote:
> On Wed, Feb 02, 2022 at 01:01:07AM +0100, Frederic Weisbecker wrote:
> > On some rare cases, the timekeeper CPU may be delaying its jiffies
> > update duty for a while. Known causes include:
> >
> > * The timekeeper is waiting on stop_machine in a MULTI_STOP_DISABLE_IRQ
> > or MULTI_STOP_RUN state. Disabled interrupts prevent from timekeeping
> > updates while waiting for the target CPU to complete its
> > stop_machine() callback.
> >
> > * The timekeeper vcpu has VMEXIT'ed for a long while due to some overload
> > on the host.
> >
> > Detect and fix these situations with emergency timekeeping catchups.
> >
> > Original-patch-by: Paul E. McKenney <paulmck@kernel.org>
> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
>
> Nice, thank you!
>
> So I should revert your earlier patch, apply this one, and then test
> the result?
No need to revert the nohz_full fix, this new one deals with non-dynticks
issues. This way we cover every timekeeper stall situations:
_ dynticks-idle is handled on IRQ entry
_ full dynticks is handled on IRQ entry in case of CPU 0 (traditional nohz_full
timekeeper) timekeeping stall. Let's hope we won't need to handle syscalls and
faults as well but we'll see...
_ periodic ticks are now handled on the tick.
So you just need to apply this patch on your dev branch for testing.
Thanks!
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] tick: Detect and fix jiffies update stall
2022-02-02 2:19 ` Frederic Weisbecker
@ 2022-02-02 17:24 ` Paul E. McKenney
0 siblings, 0 replies; 4+ messages in thread
From: Paul E. McKenney @ 2022-02-02 17:24 UTC (permalink / raw)
To: Frederic Weisbecker; +Cc: LKML, Thomas Gleixner
On Wed, Feb 02, 2022 at 03:19:51AM +0100, Frederic Weisbecker wrote:
> On Tue, Feb 01, 2022 at 05:49:34PM -0800, Paul E. McKenney wrote:
> > On Wed, Feb 02, 2022 at 01:01:07AM +0100, Frederic Weisbecker wrote:
> > > On some rare cases, the timekeeper CPU may be delaying its jiffies
> > > update duty for a while. Known causes include:
> > >
> > > * The timekeeper is waiting on stop_machine in a MULTI_STOP_DISABLE_IRQ
> > > or MULTI_STOP_RUN state. Disabled interrupts prevent from timekeeping
> > > updates while waiting for the target CPU to complete its
> > > stop_machine() callback.
> > >
> > > * The timekeeper vcpu has VMEXIT'ed for a long while due to some overload
> > > on the host.
> > >
> > > Detect and fix these situations with emergency timekeeping catchups.
> > >
> > > Original-patch-by: Paul E. McKenney <paulmck@kernel.org>
> > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > > Cc: Thomas Gleixner <tglx@linutronix.de>
> >
> > Nice, thank you!
> >
> > So I should revert your earlier patch, apply this one, and then test
> > the result?
>
> No need to revert the nohz_full fix, this new one deals with non-dynticks
> issues. This way we cover every timekeeper stall situations:
>
> _ dynticks-idle is handled on IRQ entry
>
> _ full dynticks is handled on IRQ entry in case of CPU 0 (traditional nohz_full
> timekeeper) timekeeping stall. Let's hope we won't need to handle syscalls and
> faults as well but we'll see...
>
> _ periodic ticks are now handled on the tick.
>
> So you just need to apply this patch on your dev branch for testing.
I have pulled it in, thank you! I will beat on it.
I am guessing that this goes up some other path to mainline, so I have
marked it "EXP".
Thanx, Paul
^ permalink raw reply [flat|nested] 4+ messages in thread
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2022-02-02 0:01 [PATCH] tick: Detect and fix jiffies update stall Frederic Weisbecker
2022-02-02 1:49 ` Paul E. McKenney
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2022-02-02 17:24 ` Paul E. McKenney
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