[Xen-devel] Re: [PATCH RFC 02/12] x86/ticketlock: convert spin loop to C

["H. Peter Anvin" <hpa@xxxxxxxxx>]

On 08/06/2010 07:53 AM, Jeremy Fitzhardinge wrote:
> On 08/06/2010 05:43 AM, Jan Beulich wrote:
> > You certainly mean "the compiler currently treats this as being:" - I
> > don't think there's a guarantee it'll always be doing so.
> >
> > > for (;;) {
> > > if (inc.tickets.head == inc.tickets.tail)
> > > goto out;
> > > ...
> > > }
> > > out: barrier();
> > > }
> > >
> > > (Which would probably be a reasonable way to clarify the code.)
> > I therefore think it needs to be written this way.
> Agreed.
A call/return to an actual out-of-line function is a barrier (and will 
always be a barrier, as it is the fundamental ABI sequence points), but 
to an inline function it is not.
        -hpa

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel