linux-kernel - [PATCH RFC 06/12] x86/ticketlock: make __ticket_spin

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Message-Id: <20100717004855.BB380A3C49@abulafia.goop.org>
Date:	Tue, 13 Jul 2010 15:14:26 -0700
From:	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	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 06/12] x86/ticketlock: make __ticket_spin_trylock common

Make trylock code common regardless of ticket size.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 arch/x86/include/asm/spinlock.h       |   55 +++++++++-----------------------
 arch/x86/include/asm/spinlock_types.h |    3 ++
 2 files changed, 19 insertions(+), 39 deletions(-)

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 4f9fa24..507f83c 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -100,48 +100,25 @@ static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock)
 	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;
-
-	asm volatile("movzwl %2, %0\n\t"
-		     "cmpb %h0,%b0\n\t"
-		     "leal 0x100(%" REG_PTR_MODE "0), %1\n\t"
-		     "jne 1f\n\t"
-		     LOCK_PREFIX "cmpxchgw %w1,%2\n\t"
-		     "1:"
-		     "sete %b1\n\t"
-		     "movzbl %b1,%0\n\t"
-		     : "=&a" (tmp), "=&q" (new), "+m" (lock->slock)
-		     :
-		     : "memory", "cc");
-
-	return tmp;
-}
-#else
-static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
-{
-	unsigned tmp;
-	unsigned new;
-
-	asm volatile("movl %2,%0\n\t"
-		     "movl %0,%1\n\t"
-		     "roll $16, %0\n\t"
-		     "cmpl %0,%1\n\t"
-		     "leal 0x00010000(%" REG_PTR_MODE "0), %1\n\t"
-		     "jne 1f\n\t"
-		     LOCK_PREFIX "cmpxchgl %1,%2\n\t"
-		     "1:"
-		     "sete %b1\n\t"
-		     "movzbl %b1,%0\n\t"
-		     : "=&a" (tmp), "=&q" (new), "+m" (lock->slock)
-		     :
-		     : "memory", "cc");
-
-	return tmp;
+	union {
+		struct __raw_tickets tickets;
+		__ticketpair_t slock;
+	} tmp, new;
+	int ret;
+
+	tmp.tickets = ACCESS_ONCE(lock->tickets);
+	if (tmp.tickets.head != tmp.tickets.tail)
+		return 0;
+
+	new.slock = tmp.slock + (1 << TICKET_SHIFT);
+
+	ret = cmpxchg(&lock->ticketpair, tmp.slock, new.slock) == tmp.slock;
+	barrier();		/* just make nothing creeps before lock is claimed */
+
+	return ret;
 }
-#endif
 
 static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
 {
diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
index 4582640..48dafc3 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -9,8 +9,10 @@
 
 #if (CONFIG_NR_CPUS < 256)
 typedef u8  __ticket_t;
+typedef u16 __ticketpair_t;
 #else
 typedef u16 __ticket_t;
+typedef u32 __ticketpair_t;
 #endif
 
 #define TICKET_SHIFT	(sizeof(__ticket_t) * 8)
@@ -19,6 +21,7 @@ typedef u16 __ticket_t;
 typedef struct arch_spinlock {
 	union {
 		unsigned int slock;
+		__ticketpair_t ticketpair;
 		struct __raw_tickets {
 			__ticket_t head, tail;
 		} tickets;
-- 
1.7.1.1


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