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hrtimer: Force clock_was_set() handling for the HIGHRES=n, NOHZ=y case 

When CONFIG_HIGH_RES_TIMERS is disabled, but NOHZ is enabled then
clock_was_set() is not doing anything. With HIGHRES=n the kernel relies on
the periodic tick to update the clock offsets, but when NOHZ is enabled and
active then CPUs which are in a deep idle sleep do not have a periodic tick
which means the expiry of timers affected by clock_was_set() can be
arbitrarily delayed up to the point where the CPUs are brought out of idle
again.

Make the clock_was_set() logic unconditionaly available so that idle CPUs
are kicked out of idle to handle the update.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210713135158.288697903@linutronix.de
This commit is contained in:
Thomas Gleixner 2021-07-13 15:39:49 +02:00
parent 8c3b5e6ec0
commit e71a4153b7
1 changed files with 59 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

87
kernel/time/hrtimer.c
View File

@ -739,23 +739,7 @@ static inline int hrtimer_is_hres_enabled(void)
return hrtimer_hres_enabled;
}
/*
* Retrigger next event is called after clock was set
*
* Called with interrupts disabled via on_each_cpu()
*/
static void retrigger_next_event(void *arg)
{
struct hrtimer_cpu_base *base = this_cpu_ptr(&hrtimer_bases);
if (!__hrtimer_hres_active(base))
return;
raw_spin_lock(&base->lock);
hrtimer_update_base(base);
hrtimer_force_reprogram(base, 0);
raw_spin_unlock(&base->lock);
}
static void retrigger_next_event(void *arg);
/*
* Switch to high resolution mode
@ -781,9 +765,50 @@ static void hrtimer_switch_to_hres(void)
static inline int hrtimer_is_hres_enabled(void) { return 0; }
static inline void hrtimer_switch_to_hres(void) { }
static inline void retrigger_next_event(void *arg) { }
#endif /* CONFIG_HIGH_RES_TIMERS */
/*
* Retrigger next event is called after clock was set with interrupts
* disabled through an SMP function call or directly from low level
* resume code.
*
* This is only invoked when:
* - CONFIG_HIGH_RES_TIMERS is enabled.
* - CONFIG_NOHZ_COMMON is enabled
*
* For the other cases this function is empty and because the call sites
* are optimized out it vanishes as well, i.e. no need for lots of
* #ifdeffery.
*/
static void retrigger_next_event(void *arg)
{
struct hrtimer_cpu_base *base = this_cpu_ptr(&hrtimer_bases);
/*
* When high resolution mode or nohz is active, then the offsets of
* CLOCK_REALTIME/TAI/BOOTTIME have to be updated. Otherwise the
* next tick will take care of that.
*
* If high resolution mode is active then the next expiring timer
* must be reevaluated and the clock event device reprogrammed if
* necessary.
*
* In the NOHZ case the update of the offset and the reevaluation
* of the next expiring timer is enough. The return from the SMP
* function call will take care of the reprogramming in case the
* CPU was in a NOHZ idle sleep.
*/
if (!__hrtimer_hres_active(base) && !tick_nohz_active)
return;
raw_spin_lock(&base->lock);
hrtimer_update_base(base);
if (__hrtimer_hres_active(base))
hrtimer_force_reprogram(base, 0);
else
hrtimer_update_next_event(base);
raw_spin_unlock(&base->lock);
}
/*
* When a timer is enqueued and expires earlier than the already enqueued
@ -842,22 +867,28 @@ static void hrtimer_reprogram(struct hrtimer *timer, bool reprogram)
}
/*
* Clock realtime was set
* Clock was set. This might affect CLOCK_REALTIME, CLOCK_TAI and
* CLOCK_BOOTTIME (for late sleep time injection).
*
* Change the offset of the realtime clock vs. the monotonic
* clock.
*
* We might have to reprogram the high resolution timer interrupt. On
* SMP we call the architecture specific code to retrigger _all_ high
* resolution timer interrupts. On UP we just disable interrupts and
* call the high resolution interrupt code.
* This requires to update the offsets for these clocks
* vs. CLOCK_MONOTONIC. When high resolution timers are enabled, then this
* also requires to eventually reprogram the per CPU clock event devices
* when the change moves an affected timer ahead of the first expiring
* timer on that CPU. Obviously remote per CPU clock event devices cannot
* be reprogrammed. The other reason why an IPI has to be sent is when the
* system is in !HIGH_RES and NOHZ mode. The NOHZ mode updates the offsets
* in the tick, which obviously might be stopped, so this has to bring out
* the remote CPU which might sleep in idle to get this sorted.
*/
void clock_was_set(void)
{
#ifdef CONFIG_HIGH_RES_TIMERS
if (!hrtimer_hres_active() && !tick_nohz_active)
goto out_timerfd;
/* Retrigger the CPU local events everywhere */
on_each_cpu(retrigger_next_event, NULL, 1);
#endif
out_timerfd:
timerfd_clock_was_set();
}