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From d3a77d84a8c09c393673ead13cf2e5a52297a4e3 Mon Sep 17 00:00:00 2001
From: Gregory Haskins <ghaskins@novell.com>
Date: Fri, 3 Jul 2009 08:44:22 -0500
Subject: [PATCH] rtmutex: Adjust pi_lock usage in wakeup
commit 26ba8e4b70af50b0049ff964f9366a56f7f60293 in tip.
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From: Peter W.Morreale <pmorreale@novell.com>
In wakeup_next_waiter(), we take the pi_lock, and then find out whether
we have another waiter to add to the pending owner. We can reduce
contention on the pi_lock for the pending owner if we first obtain the
pointer to the next waiter outside of the pi_lock.
Signed-off-by: Peter W. Morreale <pmorreale@novell.com>
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
kernel/rtmutex.c | 14 +++++++++-----
1 files changed, 9 insertions(+), 5 deletions(-)
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index 6435b54..5017ecb 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -507,6 +507,7 @@ static void wakeup_next_waiter(struct rt_mutex *lock, int savestate)
{
struct rt_mutex_waiter *waiter;
struct task_struct *pendowner;
+ struct rt_mutex_waiter *next;
raw_spin_lock(¤t->pi_lock);
@@ -569,6 +570,12 @@ static void wakeup_next_waiter(struct rt_mutex *lock, int savestate)
* waiter with higher priority than pending-owner->normal_prio
* is blocked on the unboosted (pending) owner.
*/
+
+ if (rt_mutex_has_waiters(lock))
+ next = rt_mutex_top_waiter(lock);
+ else
+ next = NULL;
+
raw_spin_lock(&pendowner->pi_lock);
WARN_ON(!pendowner->pi_blocked_on);
@@ -577,12 +584,9 @@ static void wakeup_next_waiter(struct rt_mutex *lock, int savestate)
pendowner->pi_blocked_on = NULL;
- if (rt_mutex_has_waiters(lock)) {
- struct rt_mutex_waiter *next;
-
- next = rt_mutex_top_waiter(lock);
+ if (next)
plist_add(&next->pi_list_entry, &pendowner->pi_waiters);
- }
+
raw_spin_unlock(&pendowner->pi_lock);
}
--
1.7.0.4
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