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x86, ticketlock: Convert __ticket_spin_lock to use xadd() 

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>
Link: http://lkml.kernel.org/r/4E5BCC40.3030501@goop.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Jeremy Fitzhardinge 2010-07-13 14:07:45 -07:00 committed by H. Peter Anvin
parent c576a3ea90
commit 2994488fe5
1 changed files with 5 additions and 30 deletions
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35
arch/x86/include/asm/spinlock.h
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@ -54,26 +54,22 @@
* 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;
@ -101,27 +97,6 @@ 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;