Re: [PATCH 4/4] locking: Introduce smp_cond_acquire()

Peter Zijlstra
2015-11-02T20:40:48Z

On Mon, Nov 02, 2015 at 08:36:49PM +0000, David Howells wrote:
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> > > + smp_read_barrier_depends(); /* ctrl */ \
> > > + smp_rmb(); /* ctrl + rmb := acquire */ \
>
> Doesn't smp_rmb() imply an smp_read_barrier_depends() anyway? In
> memory-barriers.txt, it says:
>
> Read memory barriers imply data dependency barriers, and so can
> substitute for them.

Yes, I noted that in a follow up email, Alpha implements both as MB. So
just the smp_rmb() is sufficient.