Re: [PATCH RFC net-next] trace: tcp: Add tracepoint for tcp_cwnd_reduction()

[Jason Xing]

On Mon, Jan 20, 2025 at 9:02 PM Breno Leitao <leitao@xxxxxxxxxx> wrote:
>
> Hello Jason,
>
> On Mon, Jan 20, 2025 at 08:08:52PM +0800, Jason Xing wrote:
> > On Mon, Jan 20, 2025 at 8:03 PM Breno Leitao <leitao@xxxxxxxxxx> wrote:
> > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > > index 4811727b8a02258ec6fa1fd129beecf7cbb0f90e..fc88c511e81bc12ec57e8dc3e9185a920d1bd079 100644
> > > --- a/net/ipv4/tcp_input.c
> > > +++ b/net/ipv4/tcp_input.c
> > > @@ -2710,6 +2710,8 @@ void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost,
> > >         if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
> > >                 return;
> > >
> > > +       trace_tcp_cwnd_reduction(sk, newly_acked_sacked, newly_lost, flag);
> > > +
> >
> > Are there any other reasons why introducing a new tracepoint here?
> > AFAIK, it can be easily replaced by a bpf related program or script to
> > monitor in the above position.
>
> In which position exactly?

I meant, in the position where you insert a one-line tracepoint, which
should be easily replaced with a bpf program (kprobe
tcp_cwnd_reduction with two checks like in the earlier if-statement).
It doesn't mean that I object to this new tracepoint, just curious if
you have other motivations.

Thanks,
Jason