Re: [PATCH net-next] net: tcp: add tracepoint skb_latency for latency monitor

[Eric Dumazet <edumazet@google.com>]

On Wed, Oct 9, 2024 at 2:17 PM Menglong Dong <menglong8.dong@gmail.com> wrote:
>
> In this commit, we introduce a new tracepoint "skb_latency", which is
> used to trace the latency on sending or receiving packet. For now, only
> TCP is supported. Maybe we should call it "tcp_latency"?
>
> There are 6 stages are introduced in this commit to trace the networking
> latency.
>
> The existing SO_TIMESTAMPING and MSG_TSTAMP_* can obtain the timestamping
> of sending and receiving packet, but it's not convenient.
>
> First, most applications didn't use this function when implement, and we
> can't make them implement it right now when networking latency happens.
>
> Second, it's inefficient, as it need to get the timestamping from the
> error queue with syscalls.
>
> Third, the timestamping it offers is not enough to analyse the latency
> on sending or receiving packet.
>
> As for me, the main usage of this tracepoint is to be hooked by my BPF
> program, and do some filter, and capture the latency that I interested
> in.
>
> Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> ---

Big NACK from my side.

Adding tcp_mstamp_refresh() all over the place is not what I call 'tracing'.