Adrian Moreno <amorenoz@xxxxxxxxxx> writes: > On 11/25/22 16:51, Ilya Maximets wrote: >> On 11/25/22 16:29, Adrian Moreno wrote: >>> >>> >>> On 11/23/22 22:22, Ilya Maximets wrote: >>>> On 11/22/22 15:03, Aaron Conole wrote: >>>>> When processing upcall commands, two groups of data are available to >>>>> userspace for processing: the actual packet data and the kernel >>>>> sw flow key data. The inclusion of the flow key allows the userspace >>>>> avoid running through the dissection again. >>>>> >>>>> However, the userspace can choose to ignore the flow key data, as is >>>>> the case in some ovs-vswitchd upcall processing. For these messages, >>>>> having the flow key data merely adds additional data to the upcall >>>>> pipeline without any actual gain. Userspace simply throws the data >>>>> away anyway. >>>> >>>> Hi, Aaron. While it's true that OVS in userpsace is re-parsing the >>>> packet from scratch and using the newly parsed key for the OpenFlow >>>> translation, the kernel-porvided key is still used in a few important >>>> places. Mainly for the compatibility checking. The use is described >>>> here in more details: >>>> https://docs.kernel.org/networking/openvswitch.html#flow-key-compatibility >>>> >>>> We need to compare the key generated in userspace with the key >>>> generated by the kernel to know if it's safe to install the new flow >>>> to the kernel, i.e. if the kernel and OVS userpsace are parsing the >>>> packet in the same way. >>>> >>> >>> Hi Ilya, >>> >>> Do we need to do that for every packet? >>> Could we send a bitmask of supported fields to userspace at feature >>> negotiation and let OVS slowpath flows that it knows the kernel won't >>> be able to handle properly? >> It's not that simple, because supported fields in a packet depend >> on previous fields in that same packet. For example, parsing TCP >> header is generally supported, but it won't be parsed for IPv6 >> fragments (even the first one), number of vlan headers will affect >> the parsing as we do not parse deeper than 2 vlan headers, etc. >> So, I'm afraid we have to have a per-packet information, unless we >> can somehow probe all the possible valid combinations of packet >> headers. >> > > Surely. I understand that we'd need more than just a bit per > field. Things like L4 on IPv6 frags would need another bit and the > number of VLAN headers would need some more. But, are these a handful > of exceptions or do we really need all the possible combinations of > headers? If it's a matter of naming a handful of corner cases I think > we could consider expressing them at initialization time and safe some > buffer space plus computation time both in kernel and userspace. I will take a bit more of a look here - there must surely be a way to express this when pulling information via DP_GET command so that we don't need to wait for a packet to come in to figure out whether we can parse it.
