netdev - Re: [PATCH bpf-next 0/7] bpf/flow_dissector: support input flags

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Date:   Wed, 24 Jul 2019 18:10:12 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Petar Penkov <ppenkov@...gle.com>
Subject: Re: [PATCH bpf-next 0/7] bpf/flow_dissector: support input flags

On Wed, Jul 24, 2019 at 1:11 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> C flow dissector supports input flags that tell it to customize parsing
> by either stopping early or trying to parse as deep as possible.
> BPF flow dissector always parses as deep as possible which is sub-optimal.
> Pass input flags to the BPF flow dissector as well so it can make the same
> decisions.
>
> Series outline:
> * remove unused FLOW_DISSECTOR_F_STOP_AT_L3 flag
> * export FLOW_DISSECTOR_F_XXX flags as uapi and pass them to BPF
>   flow dissector
> * add documentation for the export flags
> * support input flags in BPF_PROG_TEST_RUN via ctx_{in,out}
> * sync uapi to tools
> * support FLOW_DISSECTOR_F_PARSE_1ST_FRAG in selftest
> * support FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL in kernel and selftest
> * support FLOW_DISSECTOR_F_STOP_AT_ENCAP in selftest
>
> Pros:
> * makes BPF flow dissector faster by avoiding burning extra cycles
> * existing BPF progs continue to work by ignoring the flags and always
>   parsing as deep as possible
>
> Cons:
> * new UAPI which we need to support (OTOH, if we need to deprecate some
>   flags, we can just stop setting them upon calling BPF programs)
>
> Some numbers (with .repeat = 4000000 in test_flow_dissector):
>         test_flow_dissector:PASS:ipv4-frag 35 nsec
>         test_flow_dissector:PASS:ipv4-frag 35 nsec
>         test_flow_dissector:PASS:ipv4-no-frag 32 nsec
>         test_flow_dissector:PASS:ipv4-no-frag 32 nsec
>
>         test_flow_dissector:PASS:ipv6-frag 39 nsec
>         test_flow_dissector:PASS:ipv6-frag 39 nsec
>         test_flow_dissector:PASS:ipv6-no-frag 36 nsec
>         test_flow_dissector:PASS:ipv6-no-frag 36 nsec
>
>         test_flow_dissector:PASS:ipv6-flow-label 36 nsec
>         test_flow_dissector:PASS:ipv6-flow-label 36 nsec
>         test_flow_dissector:PASS:ipv6-no-flow-label 33 nsec
>         test_flow_dissector:PASS:ipv6-no-flow-label 33 nsec
>
>         test_flow_dissector:PASS:ipip-encap 38 nsec
>         test_flow_dissector:PASS:ipip-encap 38 nsec
>         test_flow_dissector:PASS:ipip-no-encap 32 nsec
>         test_flow_dissector:PASS:ipip-no-encap 32 nsec
>
> The improvement is around 10%, but it's in a tight cache-hot
> BPF_PROG_TEST_RUN loop.
>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Petar Penkov <ppenkov@...gle.com>

This looks great to me. Thanks, Stan!

Acked-by: Willem de Bruijn <willemb@...gle.com>