[Xen-devel] Re: [PATCH 03/20] x86/ticketlock: Use C for __ticket_spin_unlock

[AmÃrico Wang <xiyou.wangcong@xxxxxxxxx>]

On Wed, Nov 03, 2010 at 10:59:44AM -0400, Jeremy Fitzhardinge wrote:
>  * 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");

This 'if/else' really should be done with #ifdef, even though
the compiler may be smart enough to remove it.

>+
>+}
> #else
>-# define UNLOCK_LOCK_PREFIX
>+static __always_inline void __ticket_unlock_release(struct arch_spinlock 
>*lock)
>+{
>+      barrier();
>+      lock->tickets.head++;
>+      barrier();

The second barrier() is not needed.

Thanks.

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