On Fri, Jan 29, 2016 at 05:26:47PM -0800, Jarno Rajahalme wrote:
> 
> > On Jan 29, 2016, at 5:09 PM, Ben Pfaff <b...@ovn.org> wrote:
> > 
> > On Fri, Jan 29, 2016 at 03:38:12PM -0800, Jarno Rajahalme wrote:
> >> Handle implicit recirculation explicitly for each action type, so that
> >> it is easier to follow what is happening.
> >> 
> >> Signed-off-by: Jarno Rajahalme <ja...@ovn.org>
> > 
> > I think this would benefit from passing 'end' instead of 'rem_len' to
> > xlate_implicit_recirculation().  I think the code would be clearer.
> > Another argument is microoptimization: the compiler could in theory
> > factor calculating 'rem_len' out into xlate_implicit_recirculation()
> > anyway, but that would take a fair amount of insight, and it might even
> > conclude that it is commonly needed and always calculate it because it
> > is used so much.
> > 
> > I think this is the third way we've dealt with deciding when MPLS needs
> > recirculation.  The first way was, if I recall correctly, an MPLS
> > specific switch function in the spirit of recirc_unroll_actions().  The
> > second way is the current one.  But both of them make me unhappy.
> > Really, I find myself wondering whether this optimization is worth it.
> > How common do you think it is that a flow table pops off the last MPLS
> > label and then directly outputs to a port, without any resubmit or
> > goto_table intervening?  That's basically all you can do.  So I'm
> > inclined to drop this optimization and make compose_mpls_pop_action()
> > always recirculate if it pops off the last MPLS label.  It will be
> > a code cleanup and totally more maintainable.
> > 
> > What do you think?
> 
> I think you are right. I did not stop to think about the actual cases
> that benefit from postponing the recirculation. I’ll propose a patch
> to always recirculate after pop when the packet type changes (==
> ‘was_mpls’).

Sweet.  Thank you.
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