Subject: Re: [RFC PATCH v2 bpf-next 00/15] xdp_flow: Flow offload to XDP

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Mon, 18 Nov 2019 11:28:51 +0100

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