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Message-ID: <20080221152717.4804.56212.stgit@novell1.haskins.net>
Date: Thu, 21 Feb 2008 10:27:17 -0500
From: Gregory Haskins <ghaskins@...ell.com>
To: mingo@...e.hu, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
rostedt@...dmis.org, linux-rt-users@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, bill.huey@...il.com,
kevin@...man.org, cminyard@...sta.com, dsingleton@...sta.com,
dwalker@...sta.com, npiggin@...e.de, dsaxena@...xity.net,
ak@...e.de, gregkh@...e.de, sdietrich@...ell.com,
pmorreale@...ell.com, mkohari@...ell.com, ghaskins@...ell.com
Subject: [PATCH [RT] 10/14] adjust pi_lock usage in wakeup
From: Peter W.Morreale <pmorreale@...ell.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.
This patch adds a measureable increase in throughput.
Signed-off-by: Peter W. Morreale <pmorreale@...ell.com>
---
kernel/rtmutex.c | 14 +++++++++-----
1 files changed, 9 insertions(+), 5 deletions(-)
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index a7ed7b2..122f143 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -505,6 +505,7 @@ 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;
spin_lock(¤t->pi_lock);
@@ -549,6 +550,12 @@ 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;
+
spin_lock(&pendowner->pi_lock);
WARN_ON(!pendowner->pi_blocked_on);
@@ -557,12 +564,9 @@ 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);
- }
+
spin_unlock(&pendowner->pi_lock);
}
--
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