linux-kernel - Re: [PATCH v3] cgroup/bpf: fast path skb BPF filtering

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Message-ID: <e729a63a-cded-da9c-3860-a90013b87e2d@gmail.com>
Date:   Wed, 15 Dec 2021 18:54:29 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     sdf@...gle.com
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] cgroup/bpf: fast path skb BPF filtering

On 12/15/21 18:24, sdf@...gle.com wrote:
> On 12/15, Pavel Begunkov wrote:
>> On 12/15/21 17:33, sdf@...gle.com wrote:
>> > On 12/15, Pavel Begunkov wrote:
>> > > On 12/15/21 16:51, sdf@...gle.com wrote:
>> > > > On 12/15, Pavel Begunkov wrote:
>> > > > > � /* Wrappers for __cgroup_bpf_run_filter_skb() guarded by cgroup_bpf_enabled. */
>> > > > > � #define BPF_CGROUP_RUN_PROG_INET_INGRESS(sk, skb)����������������� \
>> > > > > � ({����������������������������������������� \
>> > > > > ����� int __ret = 0;��������������������������������� \
>> > > > > -��� if (cgroup_bpf_enabled(CGROUP_INET_INGRESS))������������� \
>> > > > > +��� if (cgroup_bpf_enabled(CGROUP_INET_INGRESS) && sk &&������������� \
>> > > > > +������� CGROUP_BPF_TYPE_ENABLED((sk), CGROUP_INET_INGRESS))���������� \
>> > > >
>> > > > Why not add this __cgroup_bpf_run_filter_skb check to
>> > > > __cgroup_bpf_run_filter_skb? Result of sock_cgroup_ptr() is already 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 likely be
>> > > returning to it back in a few months complaining that I see measurable
>> > > 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_skb
>> > while you're at it (plus move offset initialization down?).
> 
>> Sorry but that would be waste of time. I naively hope it will be visible
>> with net at some moment (if not already), that's how it was with io_uring,
>> that's what I see in the block layer. And in anyway, if just one inlined
>> 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.

-- 
Pavel Begunkov