[PATCH v7 14/21] timer: Split out "get next timer interrupt" functionality

Anna-Maria Behnsen
2023-05-24T07:08:14Z

The functionality for getting the next timer interrupt in
get_next_timer_interrupt() is split into a separate function
fetch_next_timer_interrupt() to be usable by other call sites.

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>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
---
v6: s/splitted/split
v5: Update commit message
v4: Fix typo in comment
---
kernel/time/timer.c | 91 +++++++++++++++++++++++++--------------------
1 file changed, 50 insertions(+), 41 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index e4b50760da3f..4bb6c168d106 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1973,6 +1973,46 @@ static unsigned long next_timer_interrupt(struct timer_base *base)
return base->next_expiry;
}

+static unsigned long fetch_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 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;
+
+ /*
+ * 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 base clock is done only when @basej is past base->clk, otherwise
* base-clk might be rewind.
@@ -2005,7 +2045,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX };
unsigned long nextevt, nextevt_local, nextevt_global;
struct timer_base *base_local, *base_global;
- bool local_first, is_idle;
+ bool is_idle;

/*
* Pretend that there is no timer pending if the cpu is offline.
@@ -2020,8 +2060,11 @@ u64 get_next_timer_interrupt(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 = fetch_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
@@ -2030,21 +2073,6 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
forward_base_clk(base_local, nextevt_local, basej);
forward_base_clk(base_global, nextevt_global, basej);

- /*
- * 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
@@ -2057,6 +2085,9 @@ u64 get_next_timer_interrupt(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
@@ -2069,31 +2100,9 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
if (time_before(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);
-
tevt.local = min_t(u64, tevt.local, tevt.global);

return cmp_next_hrtimer_event(basem, tevt.local);
--
2.30.2