linux-kernel - [PATCH -tip/master 5/7] locking/mutex: Use MUTEX_SPIN_ON

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Date:	Sun, 27 Jul 2014 22:18:42 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	peterz@...radead.org, mingo@...nel.org
Cc:	jason.low2@...com, davidlohr@...com, aswin@...com,
	linux-kernel@...r.kernel.org
Subject: [PATCH -tip/master 5/7] locking/mutex: Use MUTEX_SPIN_ON_OWNER when appropriate

4badad35 (locking/mutex: Disable optimistic spinning on some
architectures) added a ARCH_SUPPORTS_ATOMIC_RMW flag to
disable the mutex optimistic feature on specific archs.

Because CONFIG_MUTEX_SPIN_ON_OWNER only depended on DEBUG and
SMP, it was ok to have the ->owner field conditional a bit
flexible. However by adding a new variable to the matter,
we can waste space with the unused field, ie: CONFIG_SMP &&
(!CONFIG_MUTEX_SPIN_ON_OWNER && !CONFIG_DEBUG_MUTEX).

Signed-off-by: Davidlohr Bueso <davidlohr@...com>
---
 include/linux/mutex.h  | 2 +-
 kernel/locking/mutex.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 8d5535c..e4c2941 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -52,7 +52,7 @@ struct mutex {
 	atomic_t		count;
 	spinlock_t		wait_lock;
 	struct list_head	wait_list;
-#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
+#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_MUTEX_SPIN_ON_OWNER)
 	struct task_struct	*owner;
 #endif
 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
index 4115fbf..5cda397 100644
--- a/kernel/locking/mutex.h
+++ b/kernel/locking/mutex.h
@@ -16,7 +16,7 @@
 #define mutex_remove_waiter(lock, waiter, ti) \
 		__list_del((waiter)->list.prev, (waiter)->list.next)
 
-#ifdef CONFIG_SMP
+#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
 static inline void mutex_set_owner(struct mutex *lock)
 {
 	lock->owner = current;
-- 
1.8.1.4

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