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Subject[PATCH 04/14] x86/ticketlock: make large and small ticket versions of spin_lock the same
Date
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

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

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.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 0170ba9..1b81809 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -70,19 +70,16 @@ 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)
goto out;
cpu_relax();
- inc.tickets.head = ACCESS_ONCE(lock->tickets.head);
+ inc.head = ACCESS_ONCE(lock->tickets.head);
}
out: barrier(); /* make sure nothing creeps before the lock is taken */
}
@@ -108,21 +105,17 @@ 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 = { .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)
goto out;
cpu_relax();
- tmp = ACCESS_ONCE(lock->tickets.head);
+ inc.head = ACCESS_ONCE(lock->tickets.head);
}
out: barrier(); /* make sure nothing creeps before the lock is taken */
}
--
1.7.2.3


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