Messages in this thread |  | | Subject | Re: fix TCP roundtrip time update code | From | Martin Josefsson <> | Date | 03 Jun 2003 19:41:11 +0200 |
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(trimmed CC line and added netdev)
On Tue, 2003-06-03 at 17:52, David Mosberger wrote: > One of those very-hard-to-track-down, trivial-to-fix kind of problems: > without this patch, TCP roundtrip time measurements will corrupt the > routing cache's RTT estimates under heavy network load (the bug causes > RTAX_RTT to go negative, but since its type is u32, you end up with a > huge positive value...). From there on, later TCP connections quickly > will go south. > > The typo was introduced 8 months ago in v1.29 of the file by the patch > entitled "Cleanup DST metrics and abstrct MSS/PMTU further".
I tested this patch and it looks like it has cured my mysterious TCP stalls.
without patch:
cache mtu 1500 rtt 479411ms rttvar 953813ms cwnd 46 advmss 1460
I see that before and during the stall if not using this patch. (rtt is never above 20ms accoring to ping)
With the patch I see normal rtt and rttvar times. Havn't seen a stall yet (~30 kernelcompiles with distcc over a sometimes congested link), will continue testing.
> ===== net/ipv4/tcp_input.c 1.36 vs edited ===== > --- 1.36/net/ipv4/tcp_input.c Mon Apr 28 09:27:57 2003 > +++ edited/net/ipv4/tcp_input.c Tue Jun 3 08:19:36 2003 > @@ -556,8 +556,8 @@ > if (m >= dst_metric(dst, RTAX_RTTVAR)) > dst->metrics[RTAX_RTTVAR-1] = m; > else > - dst->metrics[RTAX_RTT-1] -= > - (dst->metrics[RTAX_RTT-1] - m)>>2; > + dst->metrics[RTAX_RTTVAR-1] -= > + (dst->metrics[RTAX_RTTVAR-1] - m)>>2; > } > > if (tp->snd_ssthresh >= 0xFFFF) {
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