netdev - Re: [PATCH net-next] net: tcp: add tracepoint skb

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Message-ID: <CANn89iLKVh0_wkgZ-a2+Dr9xz6wOs58CE8PpwzZEH8ZHMn=jsA@mail.gmail.com>
Date: Wed, 9 Oct 2024 17:52:55 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: kuba@...nel.org, davem@...emloft.net, pabeni@...hat.com, 
	rostedt@...dmis.org, mhiramat@...nel.org, mathieu.desnoyers@...icios.com, 
	dsahern@...nel.org, yan@...udflare.com, dongml2@...natelecom.cn, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: tcp: add tracepoint skb_latency for latency monitor

On Wed, Oct 9, 2024 at 2:17 PM Menglong Dong <menglong8.dong@...il.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@...natelecom.cn>
> ---

Big NACK from my side.

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