From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next] tcp: refine pacing rate determination Date: Tue, 25 Aug 2015 11:34:04 -0700 (PDT) Message-ID: <20150825.113404.916165871303626879.davem@davemloft.net> References: <1440203882.29244.1.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, ncardwell@google.com, ycheng@google.com To: eric.dumazet@gmail.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:58755 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754825AbbHYSeF (ORCPT ); Tue, 25 Aug 2015 14:34:05 -0400 In-Reply-To: <1440203882.29244.1.camel@edumazet-glaptop2.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Date: Fri, 21 Aug 2015 17:38:02 -0700 > From: Eric Dumazet > > When TCP pacing was added back in linux-3.12, we chose > to apply a fixed ratio of 200 % against current rate, > to allow probing for optimal throughput even during > slow start phase, where cwnd can be doubled every other gRTT. > > At Google, we found it was better applying a different ratio > while in Congestion Avoidance phase. > This ratio was set to 120 %. > > We've used the normal tcp_in_slow_start() helper for a while, > then tuned the condition to select the conservative ratio > as soon as cwnd >= ssthresh/2 : > > - After cwnd reduction, it is safer to ramp up more slowly, > as we approach optimal cwnd. > - Initial ramp up (ssthresh == INFINITY) still allows doubling > cwnd every other RTT. > > Signed-off-by: Eric Dumazet Applied.