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

[Eric Dumazet <eric.dumazet@xxxxxxxxx>]

Le mercredi 03 novembre 2010 Ã 10:59 -0400, Jeremy Fitzhardinge a
Ãcrit :
> 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 |   33 ++++++++++++++++++---------------
>  1 files changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
> index 6711d36..082990a 100644
> --- a/arch/x86/include/asm/spinlock.h
> +++ b/arch/x86/include/asm/spinlock.h
> @@ -33,9 +33,23 @@
>   * 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)
> +{
> +     barrier();

technically speaking, it should be : smp_wmb()

> +     lock->tickets.head++;
> +     barrier();

Not sure you need this one.

> +}
>  #endif
>  


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