Replace this pattern in rto_start_trylock():

    !atomic_cmpxchg_acquire(*ptr, 0, new)

... with the simpler and faster:

    atomic_try_cmpxchg_acquire(*ptr, &zero, new)

The x86 CMPXCHG instruction returns success in the ZF flag, so
atomic_try_cmpxchg_acquire() saves a compare after the CMPXCHG.

No functional change intended.

Signed-off-by: David Carlier <devnexen@gmail.com>
---
 kernel/sched/rt.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4ee8faf01441..13ac94899c18 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2172,7 +2172,8 @@ static int rto_next_cpu(struct root_domain *rd)
 
 static inline bool rto_start_trylock(atomic_t *v)
 {
-	return !atomic_cmpxchg_acquire(v, 0, 1);
+	int zero = 0;
+	return atomic_try_cmpxchg_acquire(v, &zero, 1);
 }
 
 static inline void rto_start_unlock(atomic_t *v)
-- 
2.53.0

On 4/15/26 14:40, David Carlier wrote:
> Replace this pattern in rto_start_trylock():
> 
>      !atomic_cmpxchg_acquire(*ptr, 0, new)
> 
> ... with the simpler and faster:
> 
>      atomic_try_cmpxchg_acquire(*ptr, &zero, new)
> 
> The x86 CMPXCHG instruction returns success in the ZF flag, so
> atomic_try_cmpxchg_acquire() saves a compare after the CMPXCHG.
> 
> No functional change intended.
> 
> Signed-off-by: David Carlier <devnexen@gmail.com>

Reviewed-by: Uros Bizjak <ubizjak@gmail.com>

> ---
>   kernel/sched/rt.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 4ee8faf01441..13ac94899c18 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2172,7 +2172,8 @@ static int rto_next_cpu(struct root_domain *rd)
>   
>   static inline bool rto_start_trylock(atomic_t *v)
>   {
> -	return !atomic_cmpxchg_acquire(v, 0, 1);
> +	int zero = 0;
> +	return atomic_try_cmpxchg_acquire(v, &zero, 1);
>   }
>   
>   static inline void rto_start_unlock(atomic_t *v)