On Fri, Sep 28, 2012 at 04:20:51PM -0700, Jesse Gross wrote: > On Thu, Sep 27, 2012 at 5:44 PM, Simon Horman <ho...@verge.net.au> wrote: > > On Thu, Sep 27, 2012 at 04:45:22PM -0700, Jesse Gross wrote: > >> On Thu, Sep 27, 2012 at 12:05 PM, ravi kerur <rke...@gmail.com> wrote: > >> > On Thu, Sep 27, 2012 at 11:16 AM, Jesse Gross <je...@nicira.com> wrote: > >> >> On Thu, Sep 27, 2012 at 9:26 AM, Ben Pfaff <b...@nicira.com> wrote: > >> >> > On Wed, Sep 26, 2012 at 04:13:41PM +0900, Simon Horman wrote: > >> >> >> This patch provides an implementation of the non-datapath portions > >> >> >> of MPLS matches and actions. > >> >> >> > >> >> >> This patch is based on top of Ben Pfaff's series, > >> >> >> "set-field action support" > >> >> >> > >> >> >> Cc: Isaku Yamahata <yamah...@valinux.co.jp> > >> >> >> Cc: Ravi K <rke...@gmail.com> > >> >> > > >> >> > I think Ravi's full last name is "Kerur". > >> >> > > >> >> >> Signed-off-by: Simon Horman <ho...@verge.net.au> > >> >> > > >> >> > Jesse, do you have any concerns about this? I haven't read past the > >> >> > diffstat yet. But if it seems like a reasonable intermediate approach > >> >> > then I'm happy to review it. > >> >> > >> >> I don't think there is inherently anything wrong in starting with a > >> >> userspace-only approach. I have a couple of specific concerns based > >> >> on briefly skimming the patch: > >> >> * It seems like this is really the userspace half of the code which > >> >> assumes that the kernel portions will still be doing the work on the > >> >> actual packet flows. If that's the case then I don't think that > >> >> userspace support can go in independently. Otherwise, userspace > >> >> should really be self-contained and setup slow-path flows to do the > >> >> work itself. > >> > > >> > > >> > mpls userspace is completely self-contained i.e. doesn't depend on OVS > >> > kernel code. I am saying this based on implementation and testing. During > >> > testing no OVS kernel module was loaded and testing such as ping, iperf, > >> > netperf and scp executed. > >> > >> At the very least, userspace-only code shouldn't add anything to > >> either the userspace/kernel interface or odp-util.c. I also don't see > >> how any MPLS action will actually get processed. I do see that MPLS > >> actions send packets to the local port and then install a flow but I > >> think there is a misunderstanding because that doesn't make a lot of > >> sense to me. > > > > That portion is probably my handiwork. Could you give some guidance on > > a method that would work? I'm more than happy to rework things. > > Currently this is changing the userspace flow to reflect any > modifications that we want to make. This is normally correct because > then later when we want to actually output a packet (where any > modifications would get noticed) we do a comparison from the last > output and the current flow and generate any kernel actions necessary. > However, in this case we don't have any kernel actions to do MPLS > modifications so the flow changes just get ignored. > > Instead, what we need to do is set up a slow path flow to explicitly > send all MPLS packets to userspace if there is any MPLS match or > action. We don't currently have anything in this category but it > would use the same infrastructure as CFM and LACP which also need to > go to userspace since they are actually consumed there. Once the MPLS > packets are in userspace, it should actually modify them directly > rather than just change the flow.
Is the implication that packet modifications for all actions for MPLS packets would need to occur in user-space? Or in other words, the implementation of all non-MPLS actions would need to be duplicated? > >> >> * If it is truly userspace only, the handling of multiple levels of > >> >> tags > >> >> seems a little incomplete since we actually have the full packet. > >> > > >> > > >> > Can you elaborate please? > >> > >> Multiple levels of tags aren't handled, for example, when you pop a tag. > > > > Do you think that adding support for multiple levels of tags to the kernel > > is appropriate. Or should such cases be bounced to user-space? > > The kernel should support enough tags to handle the common cases. > Initially I would make this 1 but I could see it becoming 2 in the > future. However, regardless of how many tags we support it's always > possible that a greater number of tags are used than we support. I > can see three ways to handle this: > > 1. Don't support it. You can run into a similar problem with vlan > tags because it's possible to pop tags off and then do further > operations but the kernel doesn't look deep enough into the packet. > There isn't really a mechanism to deal with this today and to my > knowledge nobody has actually complained. > > 2. Handle in userspace. It's certainly a reasonable approach for corner > cases. > > 3. Some form of recirculation. Allowing the kernel to look at a > packet, pop some tags off, and then look at it again allows processing > an infinite number of tags in a manner that won't significantly affect > throughput (although each round will result in more flow setups). It > also allows use cases like pop MPLS tag and do IP routing, which is > both fairly common and can't be realistically achieved any other way > in kernel. > > If the short term goal is a kernel implementation, I would do #1 since > it's much simpler, is a strict increase in functionality from what we > have today and doesn't preclude doing #3 in the future. If you want > something more complete then you can handle the extra cases using #2. > > If it's likely that we'll be using the userspace version for a while > then it makes sense to handle all of the various cases upfront because > we'll always have all of the packets and there's really no reason not > to. > > So it depends what your goal is. My thinking is in terms of doing #1 then #2. #3 seems to add significant complexity to the kernel for corner cases. If it is useful for a variety of cases then it may be worth-while, but it seems to me to be overkill for MPLS alone. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
