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From:   Stanislav Fomichev <sdf@google.com>
Date:   Tue, 14 Dec 2021 10:04:27 -0800
Message-ID: <CAKH8qBvRG3Zdpo0ZK_Mkji52HqMa=i9ftzMykZLQB5bnz1YAPA@mail.gmail.com>
Subject: Re: [BPF PATCH for-next] cgroup/bpf: fast path for not loaded skb BPF filtering
To:     Pavel Begunkov <asml.silence@gmail.com>
Cc:     Martin KaFai Lau <kafai@fb.com>, netdev@vger.kernel.org,
        bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Song Liu <songliubraving@fb.com>, linux-kernel@vger.kernel.org
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On Tue, Dec 14, 2021 at 10:00 AM Pavel Begunkov <asml.silence@gmail.com> wrote:
>
> On 12/14/21 17:54, sdf@google.com wrote:
> > On 12/11, Pavel Begunkov wrote:
> >> On 12/11/21 01:56, Martin KaFai Lau wrote:
> >> > On Sat, Dec 11, 2021 at 01:15:05AM +0000, Pavel Begunkov wrote:
> >> > > That was the first idea, but it's still heavier than I'd wish. 0.3%-0.7%
> >> > > in profiles, something similar in reqs/s. rcu_read_lock/unlock() pair is
> >> > > cheap but anyway adds 2 barrier()s, and with bitmasks we can inline
> >> > > the check.
> >> > It sounds like there is opportunity to optimize
> >> > __cgroup_bpf_prog_array_is_empty().
> >> >
> >> > How about using rcu_access_pointer(), testing with &empty_prog_array.hdr,
> >> > and then inline it?  The cgroup prog array cannot be all
> >> > dummy_bpf_prog.prog.  If that could be the case, it should be replaced
> >> > with &empty_prog_array.hdr earlier, so please check.
> >
> >> I'd need to expose and export empty_prog_array, but that should do.
> >> Will try it out, thanks
> >
> > Note that we already use __cgroup_bpf_prog_array_is_empty in
> > __cgroup_bpf_run_filter_setsockopt/__cgroup_bpf_run_filter_getsockopt
> > for exactly the same purpose. If you happen to optimize it, pls
> > update these places as well.
>
> Just like it's already done in the patch? Or maybe you mean something else?

Ah, you already did it, looks good! I didn't scroll all the way to the
bottom and got distracted by Martin's comment about
__cgroup_bpf_prog_array_is_empty :-[