On 2019/08/16 0:46, William Tu wrote:
On Tue, Aug 13, 2019 at 5:07 AM Toshiaki Makita <toshiaki.makita1@xxxxxxxxx> wrote:This is a rough PoC for an idea to offload TC flower to XDP. * Motivation The purpose is to speed up software TC flower by using XDP. I chose TC flower because my current interest is in OVS. OVS uses TC to offload flow tables to hardware, so if TC can offload flows to XDP, OVS also can be offloaded to XDP. When TC flower filter is offloaded to XDP, the received packets are handled by XDP first, and if their protocol or something is not supported by the eBPF program, the program returns XDP_PASS and packets are passed to upper layer TC. The packet processing flow will be like this when this mechanism, xdp_flow, is used with OVS. +-------------+ | openvswitch | | kmod | +-------------+ ^ | if not match in filters (flow key or action not supported by TC) +-------------+ | TC flower | +-------------+ ^ | if not match in flow tables (flow key or action not supported by XDP) +-------------+ | XDP prog | +-------------+ ^ | incoming packetsI like this idea, some comments about the OVS AF_XDP work. Another way when using OVS AF_XDP is to serve as slow path of TC flow HW offload. For example: Userspace OVS datapath (The one used by OVS-DPDK) ^ | +------------------------------+ | OVS AF_XDP netdev | +------------------------------+ ^ | if not supported or not match in flow tables +---------------------+ | TC HW flower | +---------------------+ ^ | incoming packets So in this case it's either TC HW flower offload, or the userspace PMD OVS. Both cases should be pretty fast. I think xdp_flow can also be used by OVS AF_XDP netdev, sitting between TC HW flower and OVS AF_XDP netdev. Before the XDP program sending packet to AF_XDP socket, the xdp_flow can execute first, and if not match, then send to AF_XDP. So in your patch set, implement s.t like bpf_redirect_map(&xsks_map, index, 0);
Thanks, the concept sounds good but this is probably difficult as long as this is a TC offload, which is emulating TC. If I changed the direction and implement offload in ovs-vswitchd, it would be possible. I'll remember this optimization.
Another thing is that at each layer we are doing its own packet parsing. From your graph, first parse at XDP program, then at TC flow, then at openvswitch kmod. I wonder if we can reuse some parsing result.
That would be nice if possible... Currently I don't have any ideas to do that. Someday XDP may support more metadata for this or HW-offload like checksum. Then we can store the information and upper layers may be able to use that. Toshiaki Makita
