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 changes in functionality.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

2 files changed, 54 insertions, 2 deletions

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index c7902ca7c9f4..3892e9c8b2de 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -426,6 +426,7 @@ 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 23788100e214..6d387dbd7304 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -490,6 +490,7 @@ __next_base(struct hrtimer_cpu_base *cpu_base, unsigned int *active)
         while ((base = __next_base((cpu_base), &(active))))
 
 static ktime_t __hrtimer_next_event_base(struct hrtimer_cpu_base *cpu_base,
+                                         const struct hrtimer *exclude,
                                          unsigned int active,
                                          ktime_t expires_next)
 {
@@ -502,9 +503,24 @@ static ktime_t __hrtimer_next_event_base(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;
+
                         if (timer->is_soft)
                                 cpu_base->softirq_next_timer = timer;
                         else
@@ -548,7 +564,8 @@ __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base, unsigned int active_
         if (!cpu_base->softirq_activated && (active_mask & HRTIMER_ACTIVE_SOFT)) {
                 active = cpu_base->active_bases & HRTIMER_ACTIVE_SOFT;
                 cpu_base->softirq_next_timer = NULL;
-                expires_next = __hrtimer_next_event_base(cpu_base, active, KTIME_MAX);
+                expires_next = __hrtimer_next_event_base(cpu_base, NULL,
+                                                         active, KTIME_MAX);
 
                 next_timer = cpu_base->softirq_next_timer;
         }
@@ -556,7 +573,8 @@ __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base, unsigned int active_
         if (active_mask & HRTIMER_ACTIVE_HARD) {
                 active = cpu_base->active_bases & HRTIMER_ACTIVE_HARD;
                 cpu_base->next_timer = next_timer;
-                expires_next = __hrtimer_next_event_base(cpu_base, active, expires_next);
+                expires_next = __hrtimer_next_event_base(cpu_base, NULL, active,
+                                                         expires_next);
         }
 
         return expires_next;
@@ -1202,6 +1220,39 @@ u64 hrtimer_get_next_event(void)
 
         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)) {
+                unsigned int active;
+
+                if (!cpu_base->softirq_activated) {
+                        active = cpu_base->active_bases & HRTIMER_ACTIVE_SOFT;
+                        expires = __hrtimer_next_event_base(cpu_base, exclude,
+                                                            active, KTIME_MAX);
+                }
+                active = cpu_base->active_bases & HRTIMER_ACTIVE_HARD;
+                expires = __hrtimer_next_event_base(cpu_base, exclude, active,
+                                                    expires);
+        }
+
+        raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
+
+        return expires;
+}
 #endif
 
 static inline int hrtimer_clockid_to_base(clockid_t clock_id)