linux-kernel - [PATCH 6/7] time: Reduce timekeeper read lock hold time

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Date:	Mon, 27 Feb 2012 16:29:33 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Richard Cochran <richardcochran@...il.com>
Subject: [PATCH 6/7] time: Reduce timekeeper read lock hold time

Now that timekeeper updates are done with a shadow copy,
we can reduce the readlock hold time to only the update.

CC: Thomas Gleixner <tglx@...utronix.de>
CC: Eric Dumazet <eric.dumazet@...il.com>
CC: Richard Cochran <richardcochran@...il.com>
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
 kernel/time/timekeeping.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index ebfb037..5a444b8 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1062,7 +1062,6 @@ static void update_wall_time(void)
 	s64 remainder;
 
 	spin_lock_irqsave(&timekeeper.wlock, flags);
-	write_seqcount_begin(&timekeeper.rlock);
 
 	/* Make sure we're fully resumed: */
 	if (unlikely(timekeeping_suspended))
@@ -1145,13 +1144,18 @@ static void update_wall_time(void)
 		second_overflow();
 	}
 
-
+	write_seqcount_begin(&timekeeper.rlock);
+	/*
+	 * We have to store rlock back to tk, otherwise we'll
+	 * corrupt the timeekeerp.rlock when we copy over timekeeper
+	 */
+	tk.rlock = timekeeper.rlock;
 	timekeeper = tk;
 	timekeeper.clock->cycle_last = timekeeper.cycle_last;
 	timekeeping_update(&timekeeper, false);
+	write_seqcount_end(&timekeeper.rlock);
 
 out:
-	write_seqcount_end(&timekeeper.rlock);
 	spin_unlock_irqrestore(&timekeeper.wlock, flags);
 
 }
-- 
1.7.3.2.146.gca209

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