time: hrtimer: Introduce hrtimer_next_event_without()

The next set of changes will need to compute the time to the next
hrtimer event over all hrtimers except for the scheduler tick one.

To that end introduce a new helper function,
hrtimer_next_event_without(), for computing the time until the next
hrtimer event over all timers except for one and modify the underlying
code in __hrtimer_next_event_base() to prepare it for being called by
that new function.

No intentional code behavior changes.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

2 files changed, 44 insertions, 4 deletions

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 012c37fdb688..27f14f2cc773 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -405,6 +405,7 @@ static inline ktime_t hrtimer_get_remaining(const struct hrtimer *timer)
 }
 
 extern u64 hrtimer_get_next_event(void);
+extern u64 hrtimer_next_event_without(const struct hrtimer *exclude);
 
 extern bool hrtimer_active(const struct hrtimer *timer);
 
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index d00e85ac10d6..12a01cb6d25c 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -463,7 +463,8 @@ static inline void hrtimer_update_next_timer(struct hrtimer_cpu_base *cpu_base,
 #endif
 }
 
-static ktime_t __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base)
+static ktime_t __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base,
+					const struct hrtimer *exclude)
 {
 	struct hrtimer_clock_base *base = cpu_base->clock_base;
 	unsigned int active = cpu_base->active_bases;
@@ -479,9 +480,24 @@ static ktime_t __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base)
 
 		next = timerqueue_getnext(&base->active);
 		timer = container_of(next, struct hrtimer, node);
+		if (timer == exclude) {
+			/* Get to the next timer in the queue. */
+			struct rb_node *rbn = rb_next(&next->node);
+
+			next = rb_entry_safe(rbn, struct timerqueue_node, node);
+			if (!next)
+				continue;
+
+			timer = container_of(next, struct hrtimer, node);
+		}
 		expires = ktime_sub(hrtimer_get_expires(timer), base->offset);
 		if (expires < expires_next) {
 			expires_next = expires;
+
+			/* Skip cpu_base update if a timer is being excluded. */
+			if (exclude)
+				continue;
+
 			hrtimer_update_next_timer(cpu_base, timer);
 		}
 	}
@@ -560,7 +576,7 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
 	if (!cpu_base->hres_active)
 		return;
 
-	expires_next = __hrtimer_get_next_event(cpu_base);
+	expires_next = __hrtimer_get_next_event(cpu_base, NULL);
 
 	if (skip_equal && expires_next == cpu_base->expires_next)
 		return;
@@ -1076,7 +1092,30 @@ u64 hrtimer_get_next_event(void)
 	raw_spin_lock_irqsave(&cpu_base->lock, flags);
 
 	if (!__hrtimer_hres_active(cpu_base))
-		expires = __hrtimer_get_next_event(cpu_base);
+		expires = __hrtimer_get_next_event(cpu_base, NULL);
+
+	raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
+
+	return expires;
+}
+
+/**
+ * hrtimer_next_event_without - time until next expiry event w/o one timer
+ * @exclude:	timer to exclude
+ *
+ * Returns the next expiry time over all timers except for the @exclude one or
+ * KTIME_MAX if none of them is pending.
+ */
+u64 hrtimer_next_event_without(const struct hrtimer *exclude)
+{
+	struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
+	u64 expires = KTIME_MAX;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&cpu_base->lock, flags);
+
+	if (__hrtimer_hres_active(cpu_base))
+		expires = __hrtimer_get_next_event(cpu_base, exclude);
 
 	raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
 
@@ -1318,7 +1357,7 @@ retry:
 	__hrtimer_run_queues(cpu_base, now);
 
 	/* Reevaluate the clock bases for the next expiry */
-	expires_next = __hrtimer_get_next_event(cpu_base);
+	expires_next = __hrtimer_get_next_event(cpu_base, NULL);
 	/*
 	 * Store the new expiry value so the migration code can verify
 	 * against it.