linux-kernel - Re: [External] Re: [PATCH v4] sock: add tracepoint for send recv length

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Date:   Mon, 9 Jan 2023 21:13:06 +0800
From:   运辉崔 <cuiyunhui@...edance.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     rostedt@...dmis.org, mhiramat@...nel.org, davem@...emloft.net,
        kuba@...nel.org, pabeni@...hat.com, kuniyu@...zon.com,
        xiyou.wangcong@...il.com, duanxiongchun@...edance.com,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [External] Re: [PATCH v4] sock: add tracepoint for send recv length

On Mon, Jan 9, 2023 at 5:56 PM Eric Dumazet <edumazet@...gle.com> wrote:

>
> Note: At least for CONFIG_RETPOLINE=y and gcc 12.2, compiler adds many
> additional instructions (and additional memory reads),
> even when the trace point is not enabled.
>
> Contrary to some belief, adding a tracepoint is not always 'free'.
> tail calls for example are replaced with normal calls.
>


>         .popsection
>
> # 0 "" 2
> #NO_APP
> .L106:
> # net/socket.c:1008: }
>         movl    %ebx, %eax      # <retval>,
>         popq    %rbx    #
>         popq    %rbp    #
>         popq    %r12    #
>         ret
> .L111:
> # ./include/trace/events/sock.h:308: DEFINE_EVENT(sock_msg_length,
> sock_recv_length,
>

Hi Eric,  Thanks for your reply,  In fact, it is because the
definition of the tracepoint function is inline,
Not just these two tracepoints，right?

#define __DECLARE_TRACE(name, proto, args, cond, data_proto)            \
      ...
      static inline void trace_##name(proto)

Regarding the above issue, I plan to optimize it like this:

static noinline void call_trace_sock_send_length(struct sock *sk, __u16 family,
                                            __u16 protocol, int ret, int flags)
{
        trace_sock_send_length(sk, family, protocol, ret, 0);
}

static inline int sock_sendmsg_nosec(struct socket *sock, struct msghdr *msg)
{
        int ret = INDIRECT_CALL_INET(sock->ops->sendmsg, inet6_sendmsg,
                                     inet_sendmsg, sock, msg,
                                     msg_data_left(msg));
        BUG_ON(ret == -EIOCBQUEUED);

        if (trace_sock_send_length_enabled()) {
                call_trace_sock_send_length(sock->sk, sock->sk->sk_family,
                                            sock->sk->sk_protocol, ret, 0);
        }
        return ret;
}

What do you think?

Thanks,
Yunhui