Re: [PATCH v2] rwsem: Support optimistic spinning

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Apr 28, 2014 at 03:09:01PM -0700, Davidlohr Bueso wrote:
> @@ -26,6 +27,10 @@ struct rw_semaphore {
>  	long			count;
>  	raw_spinlock_t		wait_lock;
>  	struct list_head	wait_list;
> +#ifdef CONFIG_SMP
> +	struct task_struct	     *owner; /* write owner */
> +	struct optimistic_spin_queue *osq;   /* spinner MCS lock */
> +#endif
>  #ifdef CONFIG_DEBUG_LOCK_ALLOC
>  	struct lockdep_map	dep_map;
>  #endif
> @@ -55,11 +60,21 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
>  # define __RWSEM_DEP_MAP_INIT(lockname)
>  #endif
>  
> +#ifdef CONFIG_SMP
> +#define __RWSEM_INITIALIZER(name)			\
> +	{ RWSEM_UNLOCKED_VALUE,				\
> +	  __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),	\
> +	  LIST_HEAD_INIT((name).wait_list),		\
> +	  NULL, /* owner */				\
> +	  NULL /* mcs lock */                           \
> +	  __RWSEM_DEP_MAP_INIT(name) }
> +#else
>  #define __RWSEM_INITIALIZER(name)			\
>  	{ RWSEM_UNLOCKED_VALUE,				\
>  	  __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),	\
>  	  LIST_HEAD_INIT((name).wait_list)		\
>  	  __RWSEM_DEP_MAP_INIT(name) }
> +#endif

I'm not saying you should change this; but something like:

#ifdef CONFIG_SMP
# define __RWSEM_SMP_INIT(name)	, .owner = NULL, .osq = NULL
#else
# define __RWSEM_SMP_INIT(name)
#endif

#define __RWSEM_INITIALIZER(name)	{			\
	.count = RWSEM_UNLOCKED_VALUE,				\
	.wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),	\
	.wait_list = LIST_HEAD_INIT(name.wait_list)		\
	__RWSEM_SMP_INIT(name)					\
	__RWSEM_DEP_MAP_INIT(name)				\
}

might be more readable in general.