From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Re: [PATCH] [TCP] Sysctl: document tcp_max_ssthresh (Limited Slow-Start) Date: Fri, 18 May 2007 12:39:17 -0700 Message-ID: <464E00E5.5050801@hp.com> References: <464DE584.7030008@ev-en.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: =?ISO-8859-1?Q?Ilpo_J=E4rvinen?= , David Miller , Netdev To: Baruch Even Return-path: Received: from palrel11.hp.com ([156.153.255.246]:46164 "EHLO palrel11.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752893AbXERTkD (ORCPT ); Fri, 18 May 2007 15:40:03 -0400 In-Reply-To: <464DE584.7030008@ev-en.org> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Baruch Even wrote: > Ilpo J=E4rvinen wrote: >=20 >>Signed-off-by: Ilpo J=E4rvinen >>--- >> Documentation/networking/ip-sysctl.txt | 13 +++++++++++++ >> 1 files changed, 13 insertions(+), 0 deletions(-) >> >>diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/n= etworking/ip-sysctl.txt >>index ce16e6a..44ba8d4 100644 >>--- a/Documentation/networking/ip-sysctl.txt >>+++ b/Documentation/networking/ip-sysctl.txt >>@@ -239,6 +239,19 @@ tcp_max_orphans - INTEGER >> more aggressively. Let me to remind again: each orphan eats >> up to ~64K of unswappable memory. >>=20 >>+tcp_max_ssthresh - INTEGER >>+ Limited Slow-Start for TCP with Large Congestion Windows defined in >>+ RFC3742. Limited slow-start is a mechanism to limit grow of the >=20 >=20 > s/grow/growth/ >=20 >=20 >>+ congestion window on the region where congestion window is larger t= han >>+ tcp_max_ssthresh. A TCP connection with a large congestion window c= ould >>+ have its congestion window increased by thousand (or even more) >>+ segments per RTT by the traditional slow-start procedure which migh= t be >>+ counter-productive to TCP performance when packet losses start to >>+ occur. With limited slow-start TCP increments congestion window at >>+ most tcp_max_ssthresh/2 segments per RTT when the congestion window= is >=20 >=20 > I'm not a native English speaker but "at most" sounds a bit awkward t= o > me, maybe change it to "by no more than". But I'm sure someone can fi= nd > a better phrasing. It could be "by at most" or "by no more than" but indeed it should not = just be=20 "at most." Also, it should be "With limited slow-start TCP increments the congesti= on=20 window..." Combining with other nits yeilds: Limited Slow-Start for TCP with Large Congestion Windows is defined in = RFC3742.=20 Limited slow-start is a mechanism to limit growth of the congestion w= indow=20 when the congestion window is larger than tcp_max_ssthresh. A TCP conn= ection=20 with a large congestion window could have its congestion window increas= ed by=20 thousands of segments (or more) per RTT via the traditional slow-start=20 procedures. This might degrade TCP performance when packet losses start= to=20 occur. With limited slow-start, TCP increments the congestion window b= y at most=20 tcp_max_ssthresh/2 segments per RTT when the congestion window is is ab= ove=20 tcp_max_ssthresh. rick jones as an asside, "tcp_max_ssthresh" sounds like the maximum value ssthresh= can=20 take-on. is that correct, or is this more of a "once ssthresh is above= this,=20 behave in this new way?" If that is the case, while the horse has prob= ably left=20 the barn, perhaps another name would be better? >=20 > Baruch > - > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html