Re: [RFC PATCH 1/1] remove redundant compare, cmpxchg already does it

[Andev]

On Wed, Jun 4, 2014 at 4:38 PM, Pranith Kumar <pranith@xxxxxxxxxx> wrote:
> remove a redundant comparision
>
> Signed-off-by: Pranith Kumar <bobby.prani@xxxxxxxxx>
> ---
>  kernel/locking/rwsem-xadd.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
> index 1f99664b..6f8bd3c 100644
> --- a/kernel/locking/rwsem-xadd.c
> +++ b/kernel/locking/rwsem-xadd.c
> @@ -249,8 +249,7 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
>  {
>      if (!(count & RWSEM_ACTIVE_MASK)) {
>          /* try acquiring the write lock */
> -        if (sem->count == RWSEM_WAITING_BIAS &&
> -            cmpxchg(&sem->count, RWSEM_WAITING_BIAS,
> +        if (cmpxchg(&sem->count, RWSEM_WAITING_BIAS,
>                  RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_WAITING_BIAS) {

This was mainly done to avoid the cost of a cmpxchg in case where they
are not equal. Not sure if it really makes a difference though.

-- 
Andev
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/