Forgot to answer this part... >> It would probably require a bit of refactoring in the kernel data >> structures so they can be used without being tied to an skb. David Ahern >> did something similar for the fib. For the routing table case, that >> resulted in a significant speedup: About 2.5x-3x the performance when >> using it via XDP (depending on the number of routes in the table). > > I'm curious about how much the helper function can improve the > performance compared to XDP programs which emulates kernel feature > without using such helpers. 2.5x-3x sounds a bit slow as XDP to me, > but it can be routing specific problem. That's specific to routing; the numbers we got were roughly consistent with the routing table lookup performance reported here: https://vincent.bernat.ch/en/blog/2017-ipv4-route-lookup-linux I.e., a fib lookup takes something on the order of 30-50 ns, which eats up quite a bit of the time budget for forwarding... -Toke
