Re: [PATCH 2/4] locking/rtmutex: Use cmp-cmpxchg

Thomas Gleixner
2015-06-05T12:38:24Z

On Tue, 19 May 2015, Davidlohr Bueso wrote:

> Avoid unnecessary cmpxchg calls, all of our other locks
> use it as well.
>
> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
> ---
> kernel/locking/rtmutex.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 74188d8..1d5cc9d 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -74,7 +74,9 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
> * set up.
> */
> #ifndef CONFIG_DEBUG_RT_MUTEXES
> -# define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c)
> +# define rt_mutex_cmpxchg(l,c,n) \
> + (l->owner == c && cmpxchg(&l->owner, c, n) == c)

Errm. How does that improve stuff like rt_mutex_lock() ?

Thanks,

tglx