Re: HyStart availability in FreeBSD stack

I was taking a look into the code for rttsample and can we add calling
that rttsample callback at tcp_xmit_timer:
- https://github.com/freebsd/freebsd-src/blob/main/sys/netinet/tcp_input.c#L3682

Looks like that place is to calculate t_srtt for TCP stack for feeding
a new RTT from the recent ACK, which seems right for rttsample for
HyStart.

Thanks,
Jaeyong

2025년 3월 24일 (월) 오후 4:17, jaeyong yoo <y.jaeyong@gmail.com>님이 작성:
>
> Thanks Cheng,
>
> Yes it looks like it implements newround callback for HyStart.
> But shouldn't it also need for "rttsample" callback?
>
> Thanks,
> Jaeyong
>
> 2025년 3월 24일 (월) 오후 3:34, Cheng Cui <cc@freebsd.org>님이 작성:
> >
> >
> >
> > On Mar 20, 2025, at 16:14, jaeyong yoo <y.jaeyong@gmail.com> wrote:
> >
> > Hi net/transport,
> >
> > We are looking for using HyStart but looks like it is only implemented
> > in RACK stack but not in FreeBSD TCP Stack.
> > Is there a plan to support this in the near future?
> >
> > Thanks,
> > Jaeyong
> >
> >
> > Hi Jaeyong,
> >
> > Sorry for the delayed response. There is a patch to enable Hystart++ for the default TCP stack. If you can help test it, I think it would be very helpful to speed up its acceptance.
> >
> > https://reviews.freebsd.org/D46425
> >
> >
> > Best Regards,
> > Cheng Cui
> >
> >
> >