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SubjectRe: [External] Re: [PATCH v4] sock: add tracepoint for send recv length
On Mon, Jan 9, 2023 at 2:13 PM 运辉崔 <cuiyunhui@bytedance.com> wrote:
>
> On Mon, Jan 9, 2023 at 5:56 PM Eric Dumazet <edumazet@google.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()) {

A barrier() is needed here, with the current state of affairs.

IMO, ftrace/x86 experts should take care of this generic issue ?



> 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

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