[Xen-devel] [PATCH 03/14] x86/ticketlock: Use C for __ticket_spin_unlock

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

If we don't need to use a locked inc for unlock, then implement it in C.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 arch/x86/include/asm/spinlock.h |   32 +++++++++++++++++---------------
 1 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index f48a6e3..0170ba9 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -33,9 +33,21 @@
  * On PPro SMP or if we are using OOSTORE, we use a locked operation to unlock
  * (PPro errata 66, 92)
  */
-# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
+static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
+{
+       if (sizeof(lock->tickets.head) == sizeof(u8))
+               asm (LOCK_PREFIX "incb %0"
+                    : "+m" (lock->tickets.head) : : "memory");
+       else
+               asm (LOCK_PREFIX "incw %0"
+                    : "+m" (lock->tickets.head) : : "memory");
+
+}
 #else
-# define UNLOCK_LOCK_PREFIX
+static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
+{
+       lock->tickets.head++;
+}
 #endif
 
 /*
@@ -93,14 +105,6 @@ static __always_inline int 
__ticket_spin_trylock(arch_spinlock_t *lock)
 
        return tmp;
 }
-
-static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
-{
-       asm volatile(UNLOCK_LOCK_PREFIX "incb %0"
-                    : "+m" (lock->slock)
-                    :
-                    : "memory", "cc");
-}
 #else
 static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
 {
@@ -144,15 +148,13 @@ static __always_inline int 
__ticket_spin_trylock(arch_spinlock_t *lock)
 
        return tmp;
 }
+#endif
 
 static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
 {
-       asm volatile(UNLOCK_LOCK_PREFIX "incw %0"
-                    : "+m" (lock->slock)
-                    :
-                    : "memory", "cc");
+       __ticket_unlock_release(lock);
+       barrier();              /* prevent reordering into locked region */
 }
-#endif
 
 static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
 {
-- 
1.7.2.3


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