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

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Message-Id: <Yboy2WwaREgo95dy@google.com>
Date:   Wed, 15 Dec 2021 10:24:25 -0800
From:   sdf@...gle.com
To:     Pavel Begunkov <asml.silence@...il.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, 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.