[ovs-dev] [RFC PATCH 4/4] Add packet recirculation

[Jesse Gross]

On Fri, Mar 22, 2013 at 6:44 AM, Simon Horman <horms at verge.net.au> wrote:
> On Tue, Mar 19, 2013 at 09:01:27AM -0700, Jesse Gross wrote:
>> On Mon, Mar 18, 2013 at 6:34 PM, Simon Horman <horms at verge.net.au> wrote:
>> > On Mon, Mar 18, 2013 at 01:49:43PM -0700, Jesse Gross wrote:
>> >> However, do we actually want to tie this directly to recirculation as
>> >> opposed to as a separate action?  I see possible benefits of
>> >> separating it out:
>> >
>> > I'm not really sure that I understand. Could you explain
>> > how you see this working?
>>
>> Just a set action plus recirculation with no argument.  Separating out
>> the issues of reusing skb mark, this could be done today with
>> something like:
>> pass 1: match MPLS -> pop_mpls, set(mark(X)), recirculate
>> pass 2: match mark X, match MPLS -> pop_mpls, recirculate
>> pass 3: match mark X, match IP -> output
>
> Thanks, I have a crude implementation of this working locally.
>
> I'm not sure what the implications are for the user-space datapath.
> Though that is less of a priority for me than the kernel datapath.

I think we could probably just add some kind of mark equivalent to the
userspace datapath.  It doesn't seem like it should be too difficult.

> I am also concerned, though less so, about:
>
> * How to handle packet_out. Perhaps some kind of synthetic facet?
> * How to detect if recirculation will occur and thus force
>   a miss to be handled with a facet. For now I am just checking
>   if the packet MPLS or not, but it would be nice not to force facets
>   unless necessary. Actually, it would be nice not to force the
>   use of facets at all.

Long term, the right optimization is probably to handle all
recirculation in userspace for these cases.  It will certainly help
performance in situations without facets since that means that we're
already stressed on flow setups and it would be good to not generate
more trips through the kernel.  However, for the time being the best
strategy seems like some kind of delayed allocation of facets to the
time that we decide to do recirculation (unless we were going to
create one anyways).