On Thu, Oct 03, 2019 at 06:33:15AM -0700, Paul E. McKenney wrote:
> On Thu, Oct 03, 2019 at 09:08:50AM -0400, Steven Rostedt wrote:
> > On Thu, 03 Oct 2019 09:39:17 +0100
> > David Howells <dhowe...@redhat.com> wrote:
> >
> > > paul...@kernel.org wrote:
> > >
> > > > +#define rcu_replace(rcu_ptr, ptr, c)
> > > > \
> > > > +({
> > > > \
> > > > + typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c));
> > > > \
> > > > + rcu_assign_pointer((rcu_ptr), (ptr));
> > > > \
> > > > + __tmp;
> > > > \
> > > > +})
> > >
> > > Does it make sense to actually use xchg() if that's supported by the arch?
>
> Historically, xchg() has been quite a bit slower than a pair of assignment
> statements, in part due to the strong memory ordering guaranteed by
> xchg(). Has that changed? If so, then, agreed, it might make sense to
> use xchg().
Nope, still the case. xchg() is an atomic op with full ordering.
