XDP sockets fallback #5995
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XDP sockets fallback #5995
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Fixes a design flaw where the xdp and sock tiles hardcode the flow steering rules for the app tiles. Defines a generic 'topo_net_rx' struct that maps UDP ports to output links (and metadata like DST_PROTO IDs). Adds a 'find_16x16' API for AVX-accelerated fast port matching. Temporarily undoes the 'repair ping-pong' flow steering hack.
Forwards ping frames arriving at the 'repair ingress' port from the shred tile to the repair tile. This was previously done at the net tile level, but is moved to the shred/repair tiles to keep the network stack clean.
Removes the loopback XDP socket from the net tile. Also removes the ethtool-loopback configure stage. Loopback is done via a sock tile in the future.
Thanks to the socket fallback, out-of-band neighbor solicitation is no longer required. When starting up (with an empty neighbor table), Firedancer steers all packets through sockets. This socket traffic will slowely populate the neighbor table with entries, which then causes traffic to get steered over the high performance path.
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- Build entire packet in during_frag callback (fixes the need to save and restore state when transitioning from during_frag to after_frag) - Publish non-routable packets to 'fallback' link instead of dropping them
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Summary
Description
This patch improves connectivity for the XDP networking stack.
Introduces the notion of a fallback TX path for high-performance network tiles such as the XDP tile.
This will become more useful in the future for net tile alternatives like ibeth or DPDK.
In the initial version of the fallback TX path, the XDP tile copies out packet data to the socket tile.
In future versions, this can be done zero-copy for improved performance.
This allows the XDP tile to drop loopback support via another XDP socket (which seems to be rather error-prone).
Performance for the loopback path will worsen but this is acceptable since loopback traffic is lower than 300k pps in prod (loopback socket throughput without offloads).
Finally, since the socket tile is now mandatory, RX connectivity generally improves:
The socket tile will handle all edge cases for packet RX that the high-performance stack failed to handle --
For example packets coming in from Wireguard or IPsec tunnels, or other hardware interfaces.
This PR depends on #5993