netdev - Re: [PATCH bpf-next v5 1/3] bpf: remove extra lock_sock for TCP_ZEROCOPY

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Message-ID: <CANn89iKv1aKE3Tcyr-vqv2mHeDompWjUn6txeK-qEO6-G-pBBw@mail.gmail.com>
Date:   Fri, 8 Jan 2021 19:40:49 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>
Subject: Re: [PATCH bpf-next v5 1/3] bpf: remove extra lock_sock for TCP_ZEROCOPY_RECEIVE

On Fri, Jan 8, 2021 at 7:26 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> On Fri, Jan 8, 2021 at 10:10 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Fri, Jan 8, 2021 at 7:03 PM Stanislav Fomichev <sdf@...gle.com> wrote:
> > >
> > > Add custom implementation of getsockopt hook for TCP_ZEROCOPY_RECEIVE.
> > > We skip generic hooks for TCP_ZEROCOPY_RECEIVE and have a custom
> > > call in do_tcp_getsockopt using the on-stack data. This removes
> > > 3% overhead for locking/unlocking the socket.
> > >
> > > Without this patch:
> > >      3.38%     0.07%  tcp_mmap  [kernel.kallsyms]  [k] __cgroup_bpf_run_filter_getsockopt
> > >             |
> > >              --3.30%--__cgroup_bpf_run_filter_getsockopt
> > >                        |
> > >                         --0.81%--__kmalloc
> > >
> > > With the patch applied:
> > >      0.52%     0.12%  tcp_mmap  [kernel.kallsyms]  [k] __cgroup_bpf_run_filter_getsockopt_kern
> > >
> >
> >
> > OK but we are adding yet another indirect call.
> >
> > Can you add a patch on top of it adding INDIRECT_CALL_INET() avoidance ?
> Sure, but do you think it will bring any benefit?

Sure, avoiding an indirect call might be the same gain than the
lock_sock() avoidance :)

> We don't have any indirect avoidance in __sys_getsockopt for the
> sock->ops->getsockopt() call.
> If we add it for this new bpf_bypass_getsockopt, we might as well add
> it for sock->ops->getsockopt?

Well, that is orthogonal to this patch.
As you may know, Google kernels do have a mitigation there already and
Brian may upstream it.

> And we need some new INDIRECT_CALL_INET2 such that f2 doesn't get
> disabled when ipv6 is disabled :-/

The same handler is called for IPv4 and IPv6, so you need the variant
with only one known handler (tcp_bpf_bypass_getsockopt)

Only it needs to make sure CONFIG_INET is enabled.