From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH v7 net-next 2/2] tcp: switch rtt estimations to usec resolution Date: Wed, 26 Feb 2014 17:04:39 -0500 (EST) Message-ID: <20140226.170439.506202474296777480.davem@davemloft.net> References: <1393292339.2316.98.camel@edumazet-glaptop2.roam.corp.google.com> <1393309341.2316.120.camel@edumazet-glaptop2.roam.corp.google.com> <1393452168.26794.8.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: stephen@networkplumber.org, ja@ssi.bg, ycheng@google.com, netdev@vger.kernel.org, ncardwell@google.com, brakmo@google.com To: eric.dumazet@gmail.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:41423 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754317AbaBZWEl (ORCPT ); Wed, 26 Feb 2014 17:04:41 -0500 In-Reply-To: <1393452168.26794.8.camel@edumazet-glaptop2.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Date: Wed, 26 Feb 2014 14:02:48 -0800 > From: Eric Dumazet > > Upcoming congestion controls for TCP require usec resolution for RTT > estimations. Millisecond resolution is simply not enough these days. > > FQ/pacing in DC environments also require this change for finer control > and removal of bimodal behavior due to the current hack in > tcp_update_pacing_rate() for 'small rtt' > > TCP_CONG_RTT_STAMP is no longer needed. > > As Julian Anastasov pointed out, we need to keep user compatibility : > tcp_metrics used to export RTT and RTTVAR in msec resolution, > so we added RTT_US and RTTVAR_US. An iproute2 patch is needed > to use the new attributes if provided by the kernel. > ... > With help from Julian Anastasov, Stephen Hemminger and Yuchung Cheng > > Signed-off-by: Eric Dumazet > Acked-by: Neal Cardwell Applied, thanks everyone.