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

From: Peter Zijlstra
Date: Thu May 08 2014 - 15:00:18 EST


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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