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>

1 files changed, 5 insertions, 30 deletions

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 5240cdefa683..b69e0b473de6 100644
--- 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;