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From:   Stanislav Fomichev <sdf@google.com>
Date:   Wed, 15 Dec 2021 11:15:05 -0800
Message-ID: <CAKH8qBv+GsPz3JTTmLZ+Q2iMSC3PS+bE1xOLbxZyjfno7hqpSA@mail.gmail.com>
Subject: Re: [PATCH v3] cgroup/bpf: fast path skb BPF filtering
To:     Pavel Begunkov <asml.silence@gmail.com>
Cc:     netdev@vger.kernel.org, bpf@vger.kernel.org,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, linux-kernel@vger.kernel.org
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On Wed, Dec 15, 2021 at 10:54 AM Pavel Begunkov <asml.silence@gmail.com> wr=
ote:
>
> On 12/15/21 18:24, sdf@google.com wrote:
> > On 12/15, Pavel Begunkov wrote:
> >> On 12/15/21 17:33, sdf@google.com wrote:
> >> > On 12/15, Pavel Begunkov wrote:
> >> > > On 12/15/21 16:51, sdf@google.com wrote:
> >> > > > On 12/15, Pavel Begunkov wrote:
> >> > > > > =EF=BF=BD /* Wrappers for __cgroup_bpf_run_filter_skb() guarde=
d by cgroup_bpf_enabled. */
> >> > > > > =EF=BF=BD #define BPF_CGROUP_RUN_PROG_INET_INGRESS(sk, skb)=EF=
=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=
=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=
 \
> >> > > > > =EF=BF=BD ({=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=
=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=
=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=
=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=
=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=
=BD=EF=BF=BD=EF=BF=BD \
> >> > > > > =EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD int __ret =3D 0;=
=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=
=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=
=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=
=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD \
> >> > > > > -=EF=BF=BD=EF=BF=BD=EF=BF=BD if (cgroup_bpf_enabled(CGROUP_INE=
T_INGRESS))=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=
=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD \
> >> > > > > +=EF=BF=BD=EF=BF=BD=EF=BF=BD if (cgroup_bpf_enabled(CGROUP_INE=
T_INGRESS) && sk &&=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=
=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD \
> >> > > > > +=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=
=BD CGROUP_BPF_TYPE_ENABLED((sk), CGROUP_INET_INGRESS))=EF=BF=BD=EF=BF=BD=
=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD \
> >> > > >
> >> > > > Why not add this __cgroup_bpf_run_filter_skb check to
> >> > > > __cgroup_bpf_run_filter_skb? Result of sock_cgroup_ptr() is alre=
ady there
> >> > > > and you can use it. Maybe move the things around if you want
> >> > > > it to happen earlier.
> >> >
> >> > > For inlining. Just wanted to get it done right, otherwise I'll lik=
ely be
> >> > > returning to it back in a few months complaining that I see measur=
able
> >> > > overhead from the function call :)
> >> >
> >> > Do you expect that direct call to bring any visible overhead?
> >> > Would be nice to compare that inlined case vs
> >> > __cgroup_bpf_prog_array_is_empty inside of __cgroup_bpf_run_filter_s=
kb
> >> > while you're at it (plus move offset initialization down?).
> >
> >> Sorry but that would be waste of time. I naively hope it will be visib=
le
> >> with net at some moment (if not already), that's how it was with io_ur=
ing,
> >> that's what I see in the block layer. And in anyway, if just one inlin=
ed
> >> won't make a difference, then 10 will.
> >
> > I can probably do more experiments on my side once your patch is
> > accepted. I'm mostly concerned with getsockopt(TCP_ZEROCOPY_RECEIVE).
> > If you claim there is visible overhead for a direct call then there
> > should be visible benefit to using CGROUP_BPF_TYPE_ENABLED there as
> > well.
>
> Interesting, sounds getsockopt might be performance sensitive to
> someone.
>
> FWIW, I forgot to mention that for testing tx I'm using io_uring
> (for both zc and not) with good submission batching.

Yeah, last time I saw 2-3% as well, but it was due to kmalloc, see
more details in 9cacf81f8161, it was pretty visible under perf.
That's why I'm a bit skeptical of your claims of direct calls being
somehow visible in these 2-3% (even skb pulls/pushes are not 2-3%?).
But tbf I don't understand how it all plays out with the io_uring.

(mostly trying to understand where there is some gain left on the
table for TCP_ZEROCOPY_RECEIVE).