linux-kernel - Re: [BPF PATCH for-next] cgroup/bpf: fast path for not loaded skb BPF filtering

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Date:   Tue, 14 Dec 2021 18:00:22 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     sdf@...gle.com
Cc:     Martin KaFai Lau <kafai@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <songliubraving@...com>, linux-kernel@...r.kernel.org
Subject: Re: [BPF PATCH for-next] cgroup/bpf: fast path for not loaded skb BPF
 filtering

On 12/14/21 17:54, sdf@...gle.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?

-- 
Pavel Begunkov