[PATCH] hrtimers: optimize softirq runqueues

The hrtimer softirq is called from the timer softirq every tick.  Retrieve the
current time from xtime and wall_to_monotonic instead of calling
base->get_time() for each timer base.  Store the time in the base structure
and provide a hook once clock source abstractions are in place and to keep the
code open for new base clocks.

Based on a patch from: Roman Zippel <zippel@linux-m68k.org>

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 26 insertions, 2 deletions

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 14bc9cfa639..b728cc53452 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -123,6 +123,26 @@ void ktime_get_ts(struct timespec *ts)
 EXPORT_SYMBOL_GPL(ktime_get_ts);
 
 /*
+ * Get the coarse grained time at the softirq based on xtime and
+ * wall_to_monotonic.
+ */
+static void hrtimer_get_softirq_time(struct hrtimer_base *base)
+{
+	ktime_t xtim, tomono;
+	unsigned long seq;
+
+	do {
+		seq = read_seqbegin(&xtime_lock);
+		xtim = timespec_to_ktime(xtime);
+		tomono = timespec_to_ktime(wall_to_monotonic);
+
+	} while (read_seqretry(&xtime_lock, seq));
+
+	base[CLOCK_REALTIME].softirq_time = xtim;
+	base[CLOCK_MONOTONIC].softirq_time = ktime_add(xtim, tomono);
+}
+
+/*
  * Functions and macros which are different for UP/SMP systems are kept in a
  * single place
  */
@@ -586,9 +606,11 @@ int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp)
  */
 static inline void run_hrtimer_queue(struct hrtimer_base *base)
 {
-	ktime_t now = base->get_time();
 	struct rb_node *node;
 
+	if (base->get_softirq_time)
+		base->softirq_time = base->get_softirq_time();
+
 	spin_lock_irq(&base->lock);
 
 	while ((node = base->first)) {
@@ -598,7 +620,7 @@ static inline void run_hrtimer_queue(struct hrtimer_base *base)
 		void *data;
 
 		timer = rb_entry(node, struct hrtimer, node);
-		if (now.tv64 <= timer->expires.tv64)
+		if (base->softirq_time.tv64 <= timer->expires.tv64)
 			break;
 
 		fn = timer->function;
@@ -641,6 +663,8 @@ void hrtimer_run_queues(void)
 	struct hrtimer_base *base = __get_cpu_var(hrtimer_bases);
 	int i;
 
+	hrtimer_get_softirq_time(base);
+
 	for (i = 0; i < MAX_HRTIMER_BASES; i++)
 		run_hrtimer_queue(&base[i]);
 }