Prev: [PATCH RFC 01/12] x86/ticketlock: clean up types and accessors
Next: [PATCH RFC 12/12] x86/pvticketlock: use callee-save for unlock_kick as well
From: Jeremy Fitzhardinge on 16 Jul 2010 21:00
Make the bulk of __ticket_spin_lock look identical for large and small
number of cpus.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge(a)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 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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Prev: [PATCH RFC 01/12] x86/ticketlock: clean up types and accessors
Next: [PATCH RFC 12/12] x86/pvticketlock: use callee-save for unlock_kick as well