On 18/02/2017 09:37, Steven Hartland wrote:
[snip]
>
> So the questions:
>
> 1. Has anyone looked at this issue before or is working on it?
> 2. Do people think we could add support for RTT estimates and enable
> receive scaling without major tcp stack changes?
We already have a non-TS-enabled RTT estimator in place c.f. the
relevant code in tcp_input.c:
if ((to.to_flags & TOF_TS) != 0 &&
to.to_tsecr) {
uint32_t t;
t = tcp_ts_getticks() - to.to_tsecr;
if (!tp->t_rttlow || tp->t_rttlow > t)
tp->t_rttlow = t;
tcp_xmit_timer(tp,
TCP_TS_TO_TICKS(t) + 1);
} else if (tp->t_rtttime &&
SEQ_GT(th->th_ack, tp->t_rtseq)) {
if (!tp->t_rttlow ||
tp->t_rttlow > ticks - tp->t_rtttime)
tp->t_rttlow = ticks - tp->t_rtttime;
tcp_xmit_timer(tp,
ticks - tp->t_rtttime);
}
The autoscaling implementation just needs to have its insistence on
using timestamps stuffed into a cannon and shot in the direction of the
sun. This is the relevant block of rcvbuf code from tcp_input.c:
if (V_tcp_do_autorcvbuf &&
(to.to_flags & TOF_TS) &&
to.to_tsecr &&
(so->so_rcv.sb_flags & SB_AUTOSIZE)) {
if (TSTMP_GT(to.to_tsecr, tp->rfbuf_ts) &&
to.to_tsecr - tp->rfbuf_ts < hz) {
if (tp->rfbuf_cnt >
(so->so_rcv.sb_hiwat / 8 * 7) &&
so->so_rcv.sb_hiwat <
V_tcp_autorcvbuf_max) {
newsize =
min(so->so_rcv.sb_hiwat +
V_tcp_autorcvbuf_inc,
V_tcp_autorcvbuf_max);
}
/* Start over with next RTT. */
tp->rfbuf_ts = 0;
tp->rfbuf_cnt = 0;
} else
tp->rfbuf_cnt += tlen; /* add up */
}
It's pretty trivial to fix by anyone so inclined.
Cheers,
Lawrence
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