[PATCH V2 2/2] hrtimer: Iterate only over active clock-bases

[Viresh Kumar]

At several instances we iterate over all possible clock-bases for a
particular cpu-base. Whereas, we only need to iterate over active bases.

We already have per cpu-base 'active_bases' field, which is updated on
addition/removal of hrtimers.

This patch creates for_each_active_base(), which uses 'active_bases' to
iterate only over active bases.

This also updates code which iterates over clock-bases.

Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
 kernel/time/hrtimer.c | 65 ++++++++++++++++++++++++++++++++-------------------
 1 file changed, 41 insertions(+), 24 deletions(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 3152f327c988..9da63e9ee63b 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -110,6 +110,31 @@ static inline int hrtimer_clockid_to_base(clockid_t clock_id)
 }
 
 
+static inline int __next_bit(unsigned int active_bases, int bit)
+{
+	do {
+		if (active_bases & (1 << bit))
+			return bit;
+	} while (++bit < HRTIMER_MAX_CLOCK_BASES);
+
+	/* We should never reach here */
+	return 0;
+}
+
+/*
+ * for_each_active_base: iterate over all active clock bases
+ * @_bit: 'int' variable for internal purpose
+ * @_base: holds pointer to a active clock base
+ * @_cpu_base: cpu base to iterate on
+ * @_active_bases: 'unsigned int' variable for internal purpose
+ */
+#define for_each_active_base(_bit, _base, _cpu_base, _active_bases)	\
+	for ((_active_bases) = (_cpu_base)->active_bases, (_bit) = -1;	\
+		(_active_bases) &&					\
+		((_bit) = __next_bit(_active_bases, ++_bit),		\
+		(_base) = (_cpu_base)->clock_base + _bit);		\
+		(_active_bases) &= ~(1 << (_bit)))
+
 /*
  * Get the coarse grained time at the softirq based on xtime and
  * wall_to_monotonic.
@@ -443,19 +468,15 @@ static inline void debug_deactivate(struct hrtimer *timer)
 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
 static ktime_t __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base)
 {
-	struct hrtimer_clock_base *base = cpu_base->clock_base;
+	struct hrtimer_clock_base *base;
 	ktime_t expires, expires_next = { .tv64 = KTIME_MAX };
+	struct hrtimer *timer;
+	unsigned int active_bases;
 	int i;
 
-	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) {
-		struct timerqueue_node *next;
-		struct hrtimer *timer;
-
-		next = timerqueue_getnext(&base->active);
-		if (!next)
-			continue;
-
-		timer = container_of(next, struct hrtimer, node);
+	for_each_active_base(i, base, cpu_base, active_bases) {
+		timer = container_of(timerqueue_getnext(&base->active),
+				     struct hrtimer, node);
 		expires = ktime_sub(hrtimer_get_expires(timer), base->offset);
 		if (expires.tv64 < expires_next.tv64)
 			expires_next = expires;
@@ -1245,6 +1266,8 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 {
 	struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
 	ktime_t expires_next, now, entry_time, delta;
+	struct hrtimer_clock_base *base;
+	unsigned int active_bases;
 	int i, retries = 0;
 
 	BUG_ON(!cpu_base->hres_active);
@@ -1264,15 +1287,10 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 	 */
 	cpu_base->expires_next.tv64 = KTIME_MAX;
 
-	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
-		struct hrtimer_clock_base *base;
+	for_each_active_base(i, base, cpu_base, active_bases) {
 		struct timerqueue_node *node;
 		ktime_t basenow;
 
-		if (!(cpu_base->active_bases & (1 << i)))
-			continue;
-
-		base = cpu_base->clock_base + i;
 		basenow = ktime_add(now, base->offset);
 
 		while ((node = timerqueue_getnext(&base->active))) {
@@ -1435,16 +1453,13 @@ void hrtimer_run_queues(void)
 	struct timerqueue_node *node;
 	struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
 	struct hrtimer_clock_base *base;
+	unsigned int active_bases;
 	int index, gettime = 1;
 
 	if (hrtimer_hres_active())
 		return;
 
-	for (index = 0; index < HRTIMER_MAX_CLOCK_BASES; index++) {
-		base = &cpu_base->clock_base[index];
-		if (!timerqueue_getnext(&base->active))
-			continue;
-
+	for_each_active_base(index, base, cpu_base, active_bases) {
 		if (gettime) {
 			hrtimer_get_softirq_time(cpu_base);
 			gettime = 0;
@@ -1665,6 +1680,8 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 static void migrate_hrtimers(int scpu)
 {
 	struct hrtimer_cpu_base *old_base, *new_base;
+	struct hrtimer_clock_base *clock_base;
+	unsigned int active_bases;
 	int i;
 
 	BUG_ON(cpu_online(scpu));
@@ -1680,9 +1697,9 @@ static void migrate_hrtimers(int scpu)
 	raw_spin_lock(&new_base->lock);
 	raw_spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
 
-	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
-		migrate_hrtimer_list(&old_base->clock_base[i],
-				     &new_base->clock_base[i]);
+	for_each_active_base(i, clock_base, old_base, active_bases) {
+		migrate_hrtimer_list(clock_base,
+				     &new_base->clock_base[clock_base->index]);
 	}
 
 	raw_spin_unlock(&old_base->lock);
-- 
2.3.0.rc0.44.ga94655d

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