[PATCH v9 23/32] timers: Retrieve next expiry of pinned/non-pinned timers separately

Anna-Maria Behnsen
2023-12-01T09:28:40Z

For the conversion of the NOHZ timer placement to a pull at expiry time
model it's required to have separate expiry times for the pinned and the
non-pinned (movable) timers. Therefore struct timer_events is introduced.

No functional change

Originally-by: Richard Cochran (linutronix GmbH) <richardcochran@gmail.com>
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
---
v9: Update was required (change of preceding patches)
---
kernel/time/timer.c | 35 +++++++++++++++++++++++++++++++----
1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 366ea26ce3ba..0d53d853ae22 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -221,6 +221,11 @@ struct timer_base {

static DEFINE_PER_CPU(struct timer_base, timer_bases[NR_BASES]);

+struct timer_events {
+ u64 local;
+ u64 global;
+};
+
#ifdef CONFIG_NO_HZ_COMMON

static DEFINE_STATIC_KEY_FALSE(timers_nohz_active);
@@ -1983,10 +1988,11 @@ static unsigned long next_timer_interrupt(struct timer_base *base,
static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
bool *idle)
{
+ struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX };
unsigned long nextevt, nextevt_local, nextevt_global;
struct timer_base *base_local, *base_global;
- u64 expires = KTIME_MAX;
bool local_first;
+ u64 expires;

/*
* Pretend that there is no timer pending if the cpu is offline.
@@ -1995,7 +2001,7 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
if (cpu_is_offline(smp_processor_id())) {
if (idle)
*idle = true;
- return expires;
+ return tevt.local;
}

base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
@@ -2022,13 +2028,31 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,

nextevt = local_first ? nextevt_local : nextevt_global;

- if (base_local->timers_pending || base_global->timers_pending) {
+ /*
+ * If the @nextevt is at max. one tick away, use @nextevt and store
+ * it in the local expiry value. The next global event is irrelevant in
+ * this case and can be left as KTIME_MAX.
+ */
+ if (time_before_eq(nextevt, basej + 1)) {
/* If we missed a tick already, force 0 delta */
if (time_before(nextevt, basej))
nextevt = basej;
- expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
+ tevt.local = basem + (u64)(nextevt - basej) * TICK_NSEC;
+ goto unlock;
}

+ /*
+ * Update tevt.* values:
+ *
+ * If the local queue expires first, then the global event can be
+ * ignored. If the global queue is empty, nothing to do either.
+ */
+ if (!local_first && base_global->timers_pending)
+ tevt.global = basem + (u64)(nextevt_global - basej) * TICK_NSEC;
+
+ if (base_local->timers_pending)
+ tevt.local = basem + (u64)(nextevt_local - basej) * TICK_NSEC;
+
/*
* We have a fresh next event. Check whether we can forward the
* base.
@@ -2058,9 +2082,12 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
trace_timer_base_idle(base_local->is_idle, base_local->cpu);
}

+unlock:
raw_spin_unlock(&base_global->lock);
raw_spin_unlock(&base_local->lock);

+ expires = min_t(u64, tevt.local, tevt.global);
+
return cmp_next_hrtimer_event(basem, expires);
}

--
2.39.2