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

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Message-ID: <CANn89iL9L_6MyZ2qYM8pGmNqjfP25mO_wMAtb7ixp+dweBS0vw@mail.gmail.com>
Date:   Fri, 8 Jan 2021 20:23:32 +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>,
        Brian Vazquez <brianvv@...gle.com>
Subject: Re: [PATCH bpf-next v5 1/3] bpf: remove extra lock_sock for TCP_ZEROCOPY_RECEIVE

On Fri, Jan 8, 2021 at 8:08 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> On Fri, Jan 8, 2021 at 10:41 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > 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.
> I guess my point here was that if I send it out only for bpf_bypass_getsockopt
> it might look a bit strange because the rest of the getsockopt still
> suffers the indirect costs.


Each new indirect call adds a cost. If you focus on optimizing
TCP_ZEROCOPY_RECEIVE,
it is counter intuitive adding an expensive indirect call.

 If Brian has plans to upstream the rest, maybe
> it's better to upstream everything together with some numbers?
> CC'ing him for his opinion.

I am just saying your point about the other indirect call is already taken care.

>
> I'm happy to follow up in whatever form is best. I can also resend
> with INDIRECT_CALL_INET2 if there are no objections in including
> this version from the start.
>

INDIRECT_CALL_INET2 seems a strange name to me.