Re: [PATCH v5] sock: add tracepoint for send recv length

[Eric Dumazet]

On Tue, Jan 10, 2023 at 10:15 AM Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx> wrote:
>
> Add 2 tracepoints to monitor the tcp/udp traffic
> of per process and per cgroup.
>
> Regarding monitoring the tcp/udp traffic of each process, there are two
> existing solutions, the first one is https://www.atoptool.nl/netatop.php.
> The second is via kprobe/kretprobe.
>
> Netatop solution is implemented by registering the hook function at the
> hook point provided by the netfilter framework.
>
> These hook functions may be in the soft interrupt context and cannot
> directly obtain the pid. Some data structures are added to bind packets
> and processes. For example, struct taskinfobucket, struct taskinfo ...
>
> Every time the process sends and receives packets it needs multiple
> hashmaps,resulting in low performance and it has the problem fo inaccurate
> tcp/udp traffic statistics(for example: multiple threads share sockets).
>
> We can obtain the information with kretprobe, but as we know, kprobe gets
> the result by trappig in an exception, which loses performance compared
> to tracepoint.
>
> We compared the performance of tracepoints with the above two methods, and
> the results are as follows:
>
> ab -n 1000000 -c 1000 -r http://127.0.0.1/index.html
> without trace:
> Time per request: 39.660 [ms] (mean)
> Time per request: 0.040 [ms] (mean, across all concurrent requests)
>
> netatop:
> Time per request: 50.717 [ms] (mean)
> Time per request: 0.051 [ms] (mean, across all concurrent requests)
>
> kr:
> Time per request: 43.168 [ms] (mean)
> Time per request: 0.043 [ms] (mean, across all concurrent requests)
>
> tracepoint:
> Time per request: 41.004 [ms] (mean)
> Time per request: 0.041 [ms] (mean, across all concurrent requests
>
> It can be seen that tracepoint has better performance.
>
> Signed-off-by: Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx>
> Signed-off-by: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx>
> ---
>  include/trace/events/sock.h | 44 +++++++++++++++++++++++++++++++++++++
>  net/socket.c                | 36 ++++++++++++++++++++++++++----
>  2 files changed, 76 insertions(+), 4 deletions(-)
>

...

> +static noinline void call_trace_sock_recv_length(struct sock *sk, int ret, int flags)
> +{
> +       trace_sock_recv_length(sk, !(flags & MSG_PEEK) ? ret :
> +                              (ret < 0 ? ret : 0), flags);

Maybe we should only 'fast assign' the two fields (ret and flags),
and let this logic happen later at 'print' time ?

This would reduce storage by one integer, and make fast path really fast.

This also could potentially remove the need for the peculiar construct with
these noinline helpers.

> +}
> +
>  static inline int sock_recvmsg_nosec(struct socket *sock, struct msghdr *msg,
>                                      int flags)


>  {
> -       return INDIRECT_CALL_INET(sock->ops->recvmsg, inet6_recvmsg,
> -                                 inet_recvmsg, sock, msg, msg_data_left(msg),
> -                                 flags);
> +       int ret = INDIRECT_CALL_INET(sock->ops->recvmsg, inet6_recvmsg,
> +                                    inet_recvmsg, sock, msg,
> +                                    msg_data_left(msg), flags);
> +
> +       if (trace_sock_recv_length_enabled())
> +               call_trace_sock_recv_length(sock->sk, !(flags & MSG_PEEK) ?
> +                                           ret : (ret < 0 ? ret : 0), flags);
> +       return ret;
>  }

Maybe you meant :

  if (trace_sock_recv_length_enabled())
      call_trace_sock_recv_length(sock->sk, ret, flags);

?

Please make sure to test your patches.