On 08/23/14 at 11:24am, Jiri Pirko wrote: > Sat, Aug 23, 2014 at 12:53:34AM CEST, sfel...@cumulusnetworks.com wrote: > > > >On Aug 22, 2014, at 12:39 PM, John Fastabend <john.fastab...@gmail.com> > >wrote: > >> - this requires OVS to be loaded to work. If all I want is > >> direct access to the hardware flow tables requiring openvswitch.ko > >> shouldn't be needed IMO. For example I may want to use the > >> hardware flow tables with something not openvswitch and we > >> shouldn't preclude that. > >> > > > >The intent is to use openvswitch.ko’s struct sw_flow to program hardware via > >the ndo_swdev_flow_* ops, but otherwise be independent of OVS. So the upper > >layer of the driver is struct sw_flow and any module above the driver can > >construct a struct sw_flow and push it down via ndo_swdev_flow_*. So your > >non-OVS use-case should be handled. OVS is another use-case. struct > >sw_flow should not be OVS-aware, but rather a generic flow match/action > >sufficient to offload the data plane to HW. > > Yes. I was thinking about simple Netlink API that would expose direct > sw_flow manipulation (ndo_swdev_flow_* wrapper) to userspace. I will > think abou that more and perhaps add it to my next patchset version.
I agree that this might help to give a better API consumption example for everyone not familiar with OVS. > >> - Also there is no programmatic way to learn which flows are > >> in hardware and which in software. There is a pr_warn but > >> that doesn't help when interacting with the hardware remotely. > >> I need some mechanism to dump the set of hardware tables and > >> the set of software tables. > > > >Agreed, we need a way to annotate which flows are installed hardware. > > Yes, we discussed that already. We need to make OVS daemon hw-offload > aware indicating which flow it want/prefers to be offloaded. This is I > believe easily extentable feature and can be added whenever the right > time is. I think the swdev flow API is good as-is. The bitmask specyfing the offload preference with all the granularity (offload-or-fail, try-to-offload, never-offload) needed can be added later, either in OVS only or in swdev itself. What is unclear in this patch is how OVS user space can know which flows are offloaded and which aren't. A status field would help here which indicates either: flow inserted and offloaded, flow inserted but not offloaded. Given that, the API consumer can easily keep track of which flows are currently offloaded. Also, I'm not sure whether flow expiration is something the API must take care of. The current proposal assumes that HW flows are only ever removed by the API itself. Could the switch CPU run code which removes flows as well? That would call for Netlink notifications. Not that it's needed at this stage of the code but maybe worth considerating for the API design. > >> - Simply duplicating the software flow/action into > >> hardware may not optimally use the hardware tables. If I have > >> a TCAM in hardware for instance. (This is how I read the patch > >> let me know if I missed something) > > > >The hardware-specific driver is the right place to handle optimizing the > >flow/action in hardware since only the driver can know the size/shape of the > >device. struct sw_flow is a generic flow description; how (or if) a flow > >gets programmed into hardware must be handled in the swdev driver. If the > >device driver can’t make the sw_flow fit into HW because of resource > >limitations or the flow simply can’t be represented in HW, then the flow is > >SW only. > > > >In the rocker driver posted in this patch set, the steps are to parse the > >struct sw_flow to figure out what type of flow match/action we’re dealing > >with (L2 or L3 or L4, ucast or mcast, ipv4 or ipv6, etc) and then install > >the correct entries into the corresponding device tables within the > >constraints of the device’s pipeline. Any optimizations, like coalescing HW > >entries, is something only the driver can do. The later examples definitely make sense and I'm not argueing against that. There is also a non hardware capabilities perspective that I would like to present: 1) TCAM capacity is limtied, we offload based on some priority assigned to flows. Some are critical and need to be in HW, others are best effort, others never go into hardware. An API user will likely want to offload best-effort flows until some watermark is reached and then switch to critical flows only. The driver is not the right place for high level optimization like this. The kernel API might but doesn't really have to either because it would mean we need APIs to transfer all of the needed context for the decision in the kernel. It might be easier to expose the hardware context to user space instead and handle these kind of optimizations in something like Quagga. 2) There is definitely a desire to allow adapting the software flow table based on the hardware capabilities. Example, given a route like this: 20.1.0.0/16, mark=50, tos=0x12, actions: output:eth1 The hardware can satisfy everything except the mark=50 match. Given a a blind 1:1 copy between hardware and software we cannot offload because a mach would be illegal. With the full context as available north of the API, this could be translated into something like this: HW: 20.1.0.0/16, tos=0x12, actions: meta=1, output:cpu SW: meta=1, mark=50, output:eth1 This will allow for partial offloads to bypass expensive masked flow table lookups by converting them into efficient flat exact match tables, offload TC classifiers, nftables or even the existing L2 and L3 forwarding path. In summary, I think the swdev API as proposed is a good start as the in-kernel flow abstraction is sufficient for many API users but we should consider enabling the model described above as well once we have the basic model put in place. I will be very interested in helping out on this for both existing classifiers and OVS flow tables. > >> - I need a way to specify put this flow/action in hardware, > >> put this flow/action in software, or put this in both software > >> and hardware. > >> > > > >This seems above the swdev layer. In other words, don’t call > >ndo_swdev_flow_* if you don’t want flow match/action install in HW. It can certainly be done northbound but this seems like a basic requirement and we might end up avoiding the code duplication and extending the API instead. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev