linux-kernel - [PATCH 05/18] x86/ticketlock: make __ticket_spin

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Date:	Wed, 24 Aug 2011 10:52:59 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: [PATCH 05/18] x86/ticketlock: make __ticket_spin_lock common

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>

Aside from the particular form of the xadd instruction, they're identical.
So factor out the xadd and use common code for the rest.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 arch/x86/include/asm/spinlock.h |   42 ++++++++++++++++++--------------------
 1 files changed, 20 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 894753f..37c3b10 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -67,13 +67,27 @@ static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
  * save some instructions and make the code more elegant. There really isn't
  * much between them in performance though, especially as locks are out of line.
  */
-#if (NR_CPUS < 256)
-static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
+static __always_inline struct __raw_tickets __ticket_spin_claim(struct arch_spinlock *lock)
 {
-	register struct __raw_tickets inc = { .tail = 1 };
+	register struct __raw_tickets tickets = { .tail = 1 };
+
+	if (sizeof(lock->tickets.head) == sizeof(u8))
+		asm volatile (LOCK_PREFIX "xaddw %w0, %1\n"
+			      : "+r" (tickets), "+m" (lock->tickets)
+			      : : "memory", "cc");
+	else
+		asm volatile (LOCK_PREFIX "xaddl %0, %1\n"
+			     : "+r" (tickets), "+m" (lock->tickets)
+			     : : "memory", "cc");
 
-	asm volatile (LOCK_PREFIX "xaddw %w0, %1\n"
-		      : "+r" (inc), "+m" (lock->tickets) : : "memory", "cc");
+	return tickets;
+}
+
+static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock)
+{
+	register struct __raw_tickets inc;
+
+	inc = __ticket_spin_claim(lock);
 
 	for (;;) {
 		if (inc.head == inc.tail)
@@ -84,6 +98,7 @@ static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
 out:	barrier();		/* make sure nothing creeps before the lock is taken */
 }
 
+#if (NR_CPUS < 256)
 static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
 {
 	unsigned int tmp, new;
@@ -103,23 +118,6 @@ static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
 	return tmp;
 }
 #else
-static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
-{
-	register struct __raw_tickets inc = { .tail = 1 };
-
-	asm volatile(LOCK_PREFIX "xaddl %0, %1\n\t"
-		     : "+r" (inc), "+m" (lock->tickets)
-		     : : "memory", "cc");
-
-	for (;;) {
-		if (inc.head == inc.tail)
-			goto out;
-		cpu_relax();
-		inc.head = ACCESS_ONCE(lock->tickets.head);
-	}
-out:	barrier();		/* make sure nothing creeps before the lock is taken */
-}
-
 static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
 {
 	unsigned tmp;
-- 
1.7.6

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