On 06.08.2010 11:00, Charles Logan wrote:
Sorry but this is not a bug. You set bad sysctl flags.
Care to explain in more detail? For example which sysctl flag was set wrong?
We won't add it to our database and this is the final decison.
Which database?
Regards,
Freebsd Team
Which team? What is your @FreeBSD.ORG address?
--
Andre
On Fri, Aug 6, 2010 at 10:56 AM, Andre Oppermann<an...@freebsd.org> wrote:
On 13.07.2010 16:01, Maxim Dounin wrote:
Hello!
On Wed, May 12, 2010 at 04:47:02PM +0400, Igor Sysoev wrote:
It seems that net.inet.tcp.slowstart_flightsize does not work in
8-STABLE.
For a long time I used slowstart_flightsize=2 on FreeBSD 4, 6, and 7
hosts.
However, FreeBSD-8 always starts with the single packet.
I saw this on different versions of 8-STABLE since 8 Oct 2009 till
04 Apr 2010.
Finally I had some time to look into it (sorry for long delay).
1. Slow start isn't used on recent FreeBSD versions for initial snd_cwnd
calculations as long as you have rfc3390 support switched on (default
since
Jan 06 23:29:46 2004, at least in 7.*). It effectively sets initial
snd_cwnd to 3*MSS on common networks and shouldn't cause any problems.
Slowstart_flightsize only affects connection restarts.
2. Due to bug in syncache code (patch below) all accepted connections has
their snd_cwnd reset to 1*MSS (since r171639, 7.0+ AFAIR).
3. Support for rfc3465 introduced in r187289 uncovered (2) as
ACK to SYN/ACK no longer causes snd_cwnd increase by MSS (actually, this
increase shouldn't happen as it's explicitly forbidden by rfc 3390, but
it's another issue). Snd_cwnd remains really small (1*MSS + 1) and this
causes really bad interaction with delayed acks on other side.
As a workaround to delayed acks interaction problems you may disable
rfc3465 by setting net.inet.tcp.rfc3465 to 0. Correct fix would be to
apply
the patch below.
To Andre Oppermann: could you please take a look at the patch and
commit it if found appropriate?
I've committed your fix with svn r210666. In a few days I will MFC it back
to the stable branches. Thanks for reporting the bug and a patch for it.
--
Andre
# HG changeset patch
# User Maxim Dounin<mdou...@mdounin.ru>
# Date 1279028684 -14400
# Node ID 93699203f408fa8e22c971769bde9c26bd14d410
# Parent e2cf8c51a6294a0d09d5628d96c6ab3ab626957e
Fix cwnd resetting problem introduced in r171639.
Sc_rxmits counts timer engagements, not actual retransmits, and value 1
corresponds to no retransmits. Revert check to correct one as present
before r171639.
diff --git a/netinet/tcp_syncache.c b/netinet/tcp_syncache.c
--- a/netinet/tcp_syncache.c
+++ b/netinet/tcp_syncache.c
@@ -804,8 +804,10 @@ syncache_socket(struct syncache *sc, str
/*
* If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
+ * Note that sc_rxmits counts timer engagements, not actual
+ * retransmits.
*/
- if (sc->sc_rxmits)
+ if (sc->sc_rxmits> 1)
tp->snd_cwnd = tp->t_maxseg;
tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
Maxim Dounin
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