From mboxrd@z Thu Jan 1 00:00:00 1970 From: Baruch Even Subject: Re: [PATCH] Too aggressive cwnd backoff Date: Thu, 07 Apr 2005 19:14:45 +0100 Message-ID: <42557895.8040004@ev-en.org> References: <20050407164146.GA6479@ev-en.org> <20050407101653.2cc68db1@dxpl.pdx.osdl.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , netdev@oss.sgi.com, Werner Almesberger Return-path: To: Stephen Hemminger In-Reply-To: <20050407101653.2cc68db1@dxpl.pdx.osdl.net> Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Stephen Hemminger wrote: > On Thu, 7 Apr 2005 19:41:46 +0300 > Baruch Even wrote: >>The provided patch will set limit to tp->ssthresh. This was the original >>behaviour in some older version of Linux. > > I think this is a real problem, and was observed by Werner with umlsim. > Don't know when it got introduced because it appears to pre-date the > '04 work in adding Westwood, BIC, Vegas. Perhaps Alexey can shed some > light on this. > > Going back to the pre-westwood code in BK, the /2 is still there. This wasn't there in 2.4.23 on which on the original work of H-TCP was done. I've encountered it in my work on the 2.6.6 version, but didn't understand all the implications at the time. I've re-encountered it now that I'm redoing the patches to 2.6.11, and it's as good a time as ever to resolve it. The effect is not catastrophic, but it does mean that we leave recovery into slow-start like ascend of cwnd until we get to ssthresh again. It does mean that after recovery we inject a lot of packets to the network at a very fast rate. Baruch