From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH 1/2] tcp: fix undo after RTO for BIC Date: Fri, 20 Jan 2012 14:18:26 -0500 (EST) Message-ID: <20120120.141826.1023767655731209208.davem@davemloft.net> References: <1326944879-22780-1-git-send-email-ncardwell@google.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, ilpo.jarvinen@helsinki.fi, nanditad@google.com, ycheng@google.com, hkchu@google.com, therbert@google.com To: ncardwell@google.com Return-path: Received: from shards.monkeyblade.net ([198.137.202.13]:32984 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754299Ab2ATTSk (ORCPT ); Fri, 20 Jan 2012 14:18:40 -0500 In-Reply-To: <1326944879-22780-1-git-send-email-ncardwell@google.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Neal Cardwell Date: Wed, 18 Jan 2012 22:47:58 -0500 > This patch fixes BIC so that cwnd reductions made during RTOs can be > undone (just as they already can be undone when using the default/Reno > behavior). > > When undoing cwnd reductions, BIC-derived congestion control modules > were restoring the cwnd from last_max_cwnd. There were two problems > with using last_max_cwnd to restore a cwnd during undo: > > (a) last_max_cwnd was set to 0 on state transitions into TCP_CA_Loss > (by calling the module's reset() functions), so cwnd reductions from > RTOs could not be undone. > > (b) when fast_covergence is enabled (which it is by default) > last_max_cwnd does not actually hold the value of snd_cwnd before the > loss; instead, it holds a scaled-down version of snd_cwnd. > > This patch makes the following changes: > > (1) upon undo, revert snd_cwnd to ca->loss_cwnd, which is already, as > the existing comment notes, the "congestion window at last loss" > > (2) stop forgetting ca->loss_cwnd on TCP_CA_Loss events > > (3) use ca->last_max_cwnd to check if we're in slow start > > Signed-off-by: Neal Cardwell Applied.