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>

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 5240cde..b69e0b4 100644 (file)
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -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;