netdev - Re: [PATCH bpf-next] bpf: don't check against device MTU in __bpf_skb_max

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Message-ID: <87ft7jzas7.fsf@toke.dk>
Date:   Tue, 15 Sep 2020 10:47:36 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Maciej Żenczykowski <maze@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, bpf <bpf@...r.kernel.org>,
        Linux NetDev <netdev@...r.kernel.org>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH bpf-next] bpf: don't check against device MTU in
 __bpf_skb_max_len

[ just jumping in to answer this bit: ]

> Would you happen to know what ebpf startup overhead is?
> How big a problem is having two (or more) back to back tc programs
> instead of one?

With a jit'ed BPF program and the in-kernel dispatcher code (which
avoids indirect calls), it's quite close to a native function call.

> We're running into both verifier performance scaling problems and code
> ownership issues with large programs...
>
> [btw. I understand for XDP we could only use 1 program anyway...]

Working on that! See my talk at LPC:
https://linuxplumbersconf.org/event/7/contributions/671/

Will post a follow-up to the list once the freplace multi-attach series
lands.

-Toke