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

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Date:   Tue, 25 Jan 2022 18:54:23 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Stanislav Fomichev <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: [PATCH v3] cgroup/bpf: fast path skb BPF filtering

On 1/24/22 18:25, Stanislav Fomichev wrote:
> On Mon, Jan 24, 2022 at 7:49 AM Pavel Begunkov <asml.silence@...il.com> wrote:
>>
>> On 12/16/21 18:24, Stanislav Fomichev wrote:
>>> On Thu, Dec 16, 2021 at 10:14 AM Martin KaFai Lau <kafai@...com> wrote:
>>>> On Thu, Dec 16, 2021 at 01:21:26PM +0000, Pavel Begunkov wrote:
>>>>> On 12/15/21 22:07, Stanislav Fomichev wrote:
>>>>>>> I'm skeptical I'll be able to measure inlining one function,
>>>>>>> variability between boots/runs is usually greater and would hide it.
>>>>>>
>>>>>> Right, that's why I suggested to mirror what we do in set/getsockopt
>>>>>> instead of the new extra CGROUP_BPF_TYPE_ENABLED. But I'll leave it up
>>>>>> to you, Martin and the rest.
>>>> I also suggested to try to stay with one way for fullsock context in v2
>>>> but it is for code readability reason.
>>>>
>>>> How about calling CGROUP_BPF_TYPE_ENABLED() just next to cgroup_bpf_enabled()
>>>> in BPF_CGROUP_RUN_PROG_*SOCKOPT_*() instead ?
>>>
>>> SG!
>>>
>>>> It is because both cgroup_bpf_enabled() and CGROUP_BPF_TYPE_ENABLED()
>>>> want to check if there is bpf to run before proceeding everything else
>>>> and then I don't need to jump to the non-inline function itself to see
>>>> if there is other prog array empty check.
>>>>
>>>> Stan, do you have concern on an extra inlined sock_cgroup_ptr()
>>>> when there is bpf prog to run for set/getsockopt()?  I think
>>>> it should be mostly noise from looking at
>>>> __cgroup_bpf_run_filter_*sockopt()?
>>>
>>> Yeah, my concern is also mostly about readability/consistency. Either
>>> __cgroup_bpf_prog_array_is_empty everywhere or this new
>>> CGROUP_BPF_TYPE_ENABLED everywhere. I'm slightly leaning towards
>>> __cgroup_bpf_prog_array_is_empty because I don't believe direct
>>> function calls add any visible overhead and macros are ugly :-) But
>>> either way is fine as long as it looks consistent.
>>
>> Martin, Stanislav, do you think it's good to go? Any other concerns?
>> It feels it might end with bikeshedding and would be great to finally
>> get it done, especially since I find the issue to be pretty simple.
> 
> I'll leave it up to the bpf maintainers/reviewers. Personally, I'd
> still prefer a respin with a consistent
> __cgroup_bpf_prog_array_is_empty or CGROUP_BPF_TYPE_ENABLED everywhere
> (shouldn't be a lot of effort?)

I can make CGROUP_BPF_TYPE_ENABLED() used everywhere, np.

I'll leave out unification with cgroup_bpf_enabled() as don't
really understand the fullsock dancing in
BPF_CGROUP_RUN_PROG_INET_EGRESS(). Any idea whether it's needed
and/or how to shove it out of inlined checks?

-- 
Pavel Begunkov