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* [PATCH] semaphore: use raw_spin_lock_irq instead of raw_spin_lock_irqsave
@ 2018-05-30 15:24 Mikulas Patocka
  2018-06-21 13:50 ` Ingo Molnar
  0 siblings, 1 reply; 6+ messages in thread
From: Mikulas Patocka @ 2018-05-30 15:24 UTC (permalink / raw)
  To: Peter Zijlstra, Ingo Molnar, Matthew Wilcox; +Cc: linux-kernel

The sleeping functions down, down_interruptible, down_killable and
down_timeout can't be called with interrupts disabled, so we don't have to
save and restore interrupt flag.

This patch avoids the costly pushf and popf instructions on the semaphore
path.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 kernel/locking/semaphore.c |   21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

Index: linux-2.6/kernel/locking/semaphore.c
===================================================================
--- linux-2.6.orig/kernel/locking/semaphore.c	2017-06-03 00:22:44.000000000 +0200
+++ linux-2.6/kernel/locking/semaphore.c	2018-05-30 14:46:35.000000000 +0200
@@ -53,14 +53,12 @@ static noinline void __up(struct semapho
  */
 void down(struct semaphore *sem)
 {
-	unsigned long flags;
-
-	raw_spin_lock_irqsave(&sem->lock, flags);
+	raw_spin_lock_irq(&sem->lock);
 	if (likely(sem->count > 0))
 		sem->count--;
 	else
 		__down(sem);
-	raw_spin_unlock_irqrestore(&sem->lock, flags);
+	raw_spin_unlock_irq(&sem->lock);
 }
 EXPORT_SYMBOL(down);
 
@@ -75,15 +73,14 @@ EXPORT_SYMBOL(down);
  */
 int down_interruptible(struct semaphore *sem)
 {
-	unsigned long flags;
 	int result = 0;
 
-	raw_spin_lock_irqsave(&sem->lock, flags);
+	raw_spin_lock_irq(&sem->lock);
 	if (likely(sem->count > 0))
 		sem->count--;
 	else
 		result = __down_interruptible(sem);
-	raw_spin_unlock_irqrestore(&sem->lock, flags);
+	raw_spin_unlock_irq(&sem->lock);
 
 	return result;
 }
@@ -101,15 +98,14 @@ EXPORT_SYMBOL(down_interruptible);
  */
 int down_killable(struct semaphore *sem)
 {
-	unsigned long flags;
 	int result = 0;
 
-	raw_spin_lock_irqsave(&sem->lock, flags);
+	raw_spin_lock_irq(&sem->lock);
 	if (likely(sem->count > 0))
 		sem->count--;
 	else
 		result = __down_killable(sem);
-	raw_spin_unlock_irqrestore(&sem->lock, flags);
+	raw_spin_unlock_irq(&sem->lock);
 
 	return result;
 }
@@ -155,15 +151,14 @@ EXPORT_SYMBOL(down_trylock);
  */
 int down_timeout(struct semaphore *sem, long timeout)
 {
-	unsigned long flags;
 	int result = 0;
 
-	raw_spin_lock_irqsave(&sem->lock, flags);
+	raw_spin_lock_irq(&sem->lock);
 	if (likely(sem->count > 0))
 		sem->count--;
 	else
 		result = __down_timeout(sem, timeout);
-	raw_spin_unlock_irqrestore(&sem->lock, flags);
+	raw_spin_unlock_irq(&sem->lock);
 
 	return result;
 }

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2018-06-21 14:28 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2018-05-30 15:24 [PATCH] semaphore: use raw_spin_lock_irq instead of raw_spin_lock_irqsave Mikulas Patocka
2018-06-21 13:50 ` Ingo Molnar
2018-06-21 14:02   ` Ingo Molnar
2018-06-21 14:17     ` Ingo Molnar
2018-06-21 14:20     ` Juergen Gross
2018-06-21 14:28       ` Ingo Molnar

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