Re: [Xen-devel] [PATCH v10 07/19] qspinlock: Use a simple write to grab the lock, if applicable

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Wed, May 07, 2014 at 11:01:35AM -0400, Waiman Long wrote:
> @@ -94,23 +94,29 @@ static inline struct mcs_spinlock *decode_tail(u32 tail)
>   * can allow better optimization of the lock acquisition for the pending
>   * bit holder.
>   */
> -#if _Q_PENDING_BITS == 8
> -
>  struct __qspinlock {
>       union {
>               atomic_t val;
> -             struct {
>  #ifdef __LITTLE_ENDIAN
> +             u8       locked;
> +             struct {
>                       u16     locked_pending;
>                       u16     tail;
> +             };
>  #else
> +             struct {
>                       u16     tail;
>                       u16     locked_pending;
> -#endif
>               };
> +             struct {
> +                     u8      reserved[3];
> +                     u8      locked;
> +             };
> +#endif
>       };
>  };
>  
> +#if _Q_PENDING_BITS == 8

That doesn't make sense, that struct __qspinlock only makes sense when
_Q_PENDING_BITS == 8.

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