linux-kernel - [PATCH 26/38] tick-sched: don't call update_wall_time() when delta is lesser than tick

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Date:	Mon, 14 Apr 2014 21:53:48 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	tglx@...utronix.de
Cc:	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, Arvind.Chauhan@....com,
	linaro-networking@...aro.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	John Stultz <john.stultz@...aro.org>
Subject: [PATCH 26/38] tick-sched: don't call update_wall_time() when delta is lesser than tick_period

In tick_do_update_jiffies64() we are processing ticks only if delta is greater
than tick_period. This is what we are supposed to do here and it broke a bit
with this patch:

commit 47a1b796306356f358e515149d86baf0cc6bf007
Author: John Stultz <john.stultz@...aro.org>
Date:   Thu Dec 12 13:10:55 2013 -0800

    tick/timekeeping: Call update_wall_time outside the jiffies lock

With above patch, we might end up calling update_wall_time() even if delta is
found to be smaller that tick_period. Fix this by reversing the check and
returning early.

Cc: John Stultz <john.stultz@...aro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 kernel/time/tick-sched.c | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index b7b09b9..bff7f97 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -65,26 +65,28 @@ static void tick_do_update_jiffies64(ktime_t now)
 	write_seqlock(&jiffies_lock);
 
 	delta = ktime_sub(now, last_jiffies_update);
-	if (delta.tv64 >= tick_period.tv64) {
-
-		delta = ktime_sub(delta, tick_period);
-		last_jiffies_update = ktime_add(last_jiffies_update,
-						tick_period);
+	if (delta.tv64 < tick_period.tv64) {
+		write_sequnlock(&jiffies_lock);
+		return;
+	}
 
-		/* Slow path for long timeouts */
-		if (unlikely(delta.tv64 >= tick_period.tv64)) {
-			s64 incr = ktime_to_ns(tick_period);
+	delta = ktime_sub(delta, tick_period);
+	last_jiffies_update = ktime_add(last_jiffies_update, tick_period);
 
-			ticks = ktime_divns(delta, incr);
+	/* Slow path for long timeouts */
+	if (unlikely(delta.tv64 >= tick_period.tv64)) {
+		s64 incr = ktime_to_ns(tick_period);
 
-			last_jiffies_update = ktime_add_ns(last_jiffies_update,
-							   incr * ticks);
-		}
-		do_timer(++ticks);
+		ticks = ktime_divns(delta, incr);
 
-		/* Keep the tick_next_period variable up to date */
-		tick_next_period = ktime_add(last_jiffies_update, tick_period);
+		last_jiffies_update = ktime_add_ns(last_jiffies_update,
+						   incr * ticks);
 	}
+	do_timer(++ticks);
+
+	/* Keep the tick_next_period variable up to date */
+	tick_next_period = ktime_add(last_jiffies_update, tick_period);
+
 	write_sequnlock(&jiffies_lock);
 	update_wall_time();
 }
-- 
1.7.12.rc2.18.g61b472e

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