Re: [PATCH] locking/rwsem: Remove arch specific rwsem files

Peter Zijlstra
2019-02-11T09:40:44Z

On Mon, Feb 11, 2019 at 10:36:01AM +0100, Peter Zijlstra wrote:
> On Sun, Feb 10, 2019 at 09:00:50PM -0500, Waiman Long wrote:
> > +static inline int __down_read_trylock(struct rw_semaphore *sem)
> > +{
> > + long tmp;
> > +
> > + while ((tmp = atomic_long_read(&sem->count)) >= 0) {
> > + if (tmp = atomic_long_cmpxchg_acquire(&sem->count, tmp,
> > + tmp + RWSEM_ACTIVE_READ_BIAS)) {
> > + return 1;
>
> That really wants to be:
>
> if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
> tmp + RWSEM_ACTIVE_READ_BIAS))
>
> > + }
> > + }
> > + return 0;
> > +}

Also, the is the one case where LL/SC can actually do 'better'. Do you
have benchmarks for say PowerPC or ARM64 ?