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

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Date:   Fri, 8 Jan 2021 10:26:40 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Eric Dumazet <edumazet@...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 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?
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?
And we need some new INDIRECT_CALL_INET2 such that f2 doesn't get
disabled when ipv6 is disabled :-/