On Aug 29, 2014, at 9:36 AM, Jarno Rajahalme <jrajaha...@nicira.com> wrote:
> > On Aug 28, 2014, at 9:32 AM, Ben Pfaff <b...@nicira.com> wrote: > >> On Fri, Aug 22, 2014 at 01:58:17PM -0700, Jarno Rajahalme wrote: >>> barrier->count is used as a simple counter and is not expected the >>> synchronize the state of any other variable, so we can use atomic_count, >>> which uses relaxed atomics. >>> >>> Ditto for the 'next_id' within ovsthread_wrapper(). >>> >>> Signed-off-by: Jarno Rajahalme <jrajaha...@nicira.com> >> >> I would have thought that ovs_barrier_block() would include a fairly >> strong barrier--at least an acquire-release barrier?--but it doesn't >> seem to necessarily include one at all now. > > Yes, it would seem reasonable to expect that the effects of all participating > threads would be visible on return from ovs_barrier_block(). Even after this > change the seq_read() does that (due to ovs_mutex_lock() and > ovs_mutex_unlock(), which have acquire and release semantics, respectively). > However, seq_read() could be implemented without using a mutex, so it would > be better to not rely on it. > I looked into this a bit more and I now think seq makes no sense without acquire-release semantics (which it already implements), so I plan to document it and then rely on it. Let’s see what you think. Jarno > I’ll post a v2 on this to address this, thanks! > > Jarno _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
