[PATCH v3 09/17] timer: Split out "get next timer interrupt" functionality

Anna-Maria Behnsen
2022-10-25T13:59:42Z

forward_and_idle_timer_bases() includes the functionality for getting the
next timer interrupt. To reuse it, it is splitted into an separate function
"get_next_timer_interrupt()".

This is preparatory work for the conversion of the NOHZ timer
placement to a pull at expiry time model. No functional change.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
---
kernel/time/timer.c | 93 +++++++++++++++++++++++++--------------------
1 file changed, 51 insertions(+), 42 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 1990eb1b2cc9..167ae89f0f46 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1704,6 +1704,46 @@ static unsigned long next_timer_interrupt(struct timer_base *base)
return base->next_expiry;
}

+static unsigned long get_next_timer_interrupt(struct timer_base *base_local,
+ struct timer_base *base_global,
+ unsigned long basej, u64 basem,
+ struct timer_events *tevt)
+{
+ unsigned long nextevt_local, nextevt_global;
+ bool local_first;
+
+ nextevt_local = next_timer_interrupt(base_local);
+ nextevt_global = next_timer_interrupt(base_global);
+
+ /*
+ * Check whether the local event is expiring before or at the same
+ * time as the global event.
+ *
+ * Note, that nextevt_global and next_evtlocal might be based on
+ * different base->clk values. So it's not guaranteed that
+ * comparing with empty bases results in a correct local_first.
+ */
+ if (base_local->timers_pending && base_global->timers_pending)
+ local_first = time_before_eq(nextevt_local, nextevt_global);
+ else
+ local_first = base_local->timers_pending;
+
+ /*
+ * 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;
+
+ return local_first ? nextevt_local : nextevt_global;
+}
+
/**
* forward_and_idle_timer_bases
* @basej: base time jiffies
@@ -1723,7 +1763,7 @@ void forward_and_idle_timer_bases(unsigned long basej, u64 basem,
{
unsigned long nextevt, nextevt_local, nextevt_global;
struct timer_base *base_local, *base_global;
- bool local_first, is_idle;
+ bool is_idle;

/* Preset local / global events */
tevt->local = tevt->global = KTIME_MAX;
@@ -1741,8 +1781,11 @@ void forward_and_idle_timer_bases(unsigned long basej, u64 basem,
raw_spin_lock(&base_local->lock);
raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);

- nextevt_local = next_timer_interrupt(base_local);
- nextevt_global = next_timer_interrupt(base_global);
+ nextevt = get_next_timer_interrupt(base_local, base_global,
+ basej, basem, tevt);
+
+ nextevt_local = base_local->next_expiry;
+ nextevt_global = base_global->next_expiry;

/*
* We have a fresh next event. Check whether we can forward the
@@ -1763,21 +1806,6 @@ void forward_and_idle_timer_bases(unsigned long basej, u64 basem,
base_global->clk = nextevt_global;
}

- /*
- * Check whether the local event is expiring before or at the same
- * time as the global event.
- *
- * Note, that nextevt_global and nextevt_local might be based on
- * different base->clk values. So it's not guaranteed that
- * comparing with empty bases results in a correct local_first.
- */
- if (base_local->timers_pending && base_global->timers_pending)
- local_first = time_before_eq(nextevt_local, nextevt_global);
- else
- local_first = base_local->timers_pending;
-
- nextevt = local_first ? nextevt_local : nextevt_global;
-
/*
* Bases are idle if the next event is more than a tick away. Also
* the tick is stopped so any added timer must forward the base clk
@@ -1790,43 +1818,24 @@ void forward_and_idle_timer_bases(unsigned long basej, u64 basem,
/* We need to mark both bases in sync */
base_local->is_idle = base_global->is_idle = is_idle;

+ raw_spin_unlock(&base_global->lock);
+ raw_spin_unlock(&base_local->lock);
+
/*
* If the bases are not marked idle, i.e one of the events is at
* max. one tick away, then the CPU can't go into a NOHZ idle
* sleep. Use the earlier event of both and store it in the local
* expiry value. The next global event is irrelevant in this case
- * and can be left as KTIME_MAX. CPU will wakeup on time.
+ * and can be reset as KTIME_MAX. CPU will wakeup on time.
*/
if (!is_idle) {
/* If we missed a tick already, force 0 delta */
if (time_before_eq(nextevt, basej))
nextevt = basej;
tevt->local = basem + (u64)(nextevt - basej) * TICK_NSEC;
- goto unlock;
+ tevt->global = KTIME_MAX;
}

- /*
- * If the bases are marked idle, i.e. the next event on both the
- * local and the global queue are farther away than a tick,
- * evaluate both bases. No need to check whether one of the bases
- * has an already expired timer as this is caught by the !is_idle
- * condition above.
- */
- if (base_local->timers_pending)
- tevt->local = basem + (u64)(nextevt_local - basej) * TICK_NSEC;
-
- /*
- * If the local queue expires first, then the global event can be
- * ignored. The CPU wakes up before that. 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;
-
-unlock:
- raw_spin_unlock(&base_global->lock);
- raw_spin_unlock(&base_local->lock);
-
cmp_next_hrtimer_event(basem, tevt);
}

--
2.30.2