linux-kernel - [PATCH RFC 04/12] x86/ticketlock: make large and small ticket versions of spin

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Date:	Fri, 16 Jul 2010 18:03:04 -0700 (PDT)
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>, Avi Kivity <avi@...hat.com>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: [PATCH RFC 04/12] x86/ticketlock: make large and small ticket versions of spin_lock the same

Make the bulk of __ticket_spin_lock look identical for large and small
number of cpus.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 arch/x86/include/asm/spinlock.h |   23 ++++++++---------------
 1 files changed, 8 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 082990a..7586d7a 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -72,19 +72,16 @@ static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
 #if (NR_CPUS < 256)
 static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
 {
-	register union {
-		struct __raw_tickets tickets;
-		unsigned short slock;
-	} inc = { .slock = 1 << TICKET_SHIFT };
+	register struct __raw_tickets inc = { .tail = 1 };
 
 	asm volatile (LOCK_PREFIX "xaddw %w0, %1\n"
-		      : "+Q" (inc), "+m" (lock->slock) : : "memory", "cc");
+		      : "+r" (inc), "+m" (lock->tickets) : : "memory", "cc");
 
 	for (;;) {
-		if (inc.tickets.head == inc.tickets.tail)
+		if (inc.head == inc.tail)
 			return;
 		cpu_relax();
-		inc.tickets.head = ACCESS_ONCE(lock->tickets.head);
+		inc.head = ACCESS_ONCE(lock->tickets.head);
 	}
 	barrier();		/* make sure nothing creeps before the lock is taken */
 }
@@ -110,21 +107,17 @@ static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
 #else
 static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
 {
-	unsigned inc = 1 << TICKET_SHIFT;
-	__ticket_t tmp;
+	register struct __raw_tickets inc = { .tickets.tail = 1 };
 
 	asm volatile(LOCK_PREFIX "xaddl %0, %1\n\t"
-		     : "+r" (inc), "+m" (lock->slock)
+		     : "+r" (inc), "+m" (lock->tickets)
 		     : : "memory", "cc");
 
-	tmp = inc;
-	inc >>= TICKET_SHIFT;
-
 	for (;;) {
-		if ((__ticket_t)inc == tmp)
+		if (inc.head == inc.tail)
 			return;
 		cpu_relax();
-		tmp = ACCESS_ONCE(lock->tickets.head);
+		inc.head = ACCESS_ONCE(lock->tickets.head);
 	}
 	barrier();		/* make sure nothing creeps before the lock is taken */
 }
-- 
1.7.1.1


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