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Subject[PATCH 11/12] x86/ticketlock: convert __ticket_spin_lock to use xadd()
Date
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

Convert the two variants of __ticket_spin_lock() to use xadd(), which
has the effect of making them identical, so remove the duplicate function.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
arch/x86/include/asm/spinlock.h | 35 +++++------------------------------
1 files changed, 5 insertions(+), 30 deletions(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 1c8a23c..adf010a 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -55,26 +55,22 @@
* 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)
{
- 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");
+ inc = xadd(&lock->tickets, inc);

for (;;) {
- if (inc.tickets.head == inc.tickets.tail)
+ if (inc.head == inc.tail)
break;
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 */
}

+#if (NR_CPUS < 256)
static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
{
unsigned int tmp, new;
@@ -102,27 +98,6 @@ static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
: "memory", "cc");
}
#else
-static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
-{
- unsigned inc = 1 << TICKET_SHIFT;
- __ticket_t tmp;
-
- asm volatile(LOCK_PREFIX "xaddl %0, %1\n\t"
- : "+r" (inc), "+m" (lock->slock)
- : : "memory", "cc");
-
- tmp = inc;
- inc >>= TICKET_SHIFT;
-
- for (;;) {
- if ((__ticket_t)inc == tmp)
- break;
- cpu_relax();
- tmp = ACCESS_ONCE(lock->tickets.head);
- }
- 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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