On Thu, Oct 03, 2019 at 03:41:31PM +0200, Peter Zijlstra wrote:
> 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.
OK, let's stick with the pair of assignments, then. ;-)
Thanx, Paul
