From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from korolev.univ-paris7.fr (korolev.univ-paris7.fr [IPv6:2001:660:3301:8000::1:2]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id DF4E121F20F for ; Wed, 30 Oct 2013 17:15:58 -0700 (PDT) Received: from mailhub.math.univ-paris-diderot.fr (mailhub.math.univ-paris-diderot.fr [81.194.30.253]) by korolev.univ-paris7.fr (8.14.4/8.14.4/relay1/46573) with ESMTP id r9V0FhJZ024465; Thu, 31 Oct 2013 01:15:43 +0100 Received: from mailhub.math.univ-paris-diderot.fr (localhost [127.0.0.1]) by mailhub.math.univ-paris-diderot.fr (Postfix) with ESMTP id 135305A86C; Thu, 31 Oct 2013 01:15:43 +0100 (CET) X-Virus-Scanned: amavisd-new at math.univ-paris-diderot.fr Received: from mailhub.math.univ-paris-diderot.fr ([127.0.0.1]) by mailhub.math.univ-paris-diderot.fr (mailhub.math.univ-paris-diderot.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id twIrJWvC7eK7; Thu, 31 Oct 2013 01:15:42 +0100 (CET) Received: from ijon.pps.jussieu.fr (unknown [78.194.40.74]) (Authenticated sender: jch) by mailhub.math.univ-paris-diderot.fr (Postfix) with ESMTPSA id 1D60E5A86F; Thu, 31 Oct 2013 01:15:42 +0100 (CET) Received: from localhost ([127.0.0.1] helo=ijon.pps.jussieu.fr) by ijon.pps.jussieu.fr with esmtp (Exim 4.80) (envelope-from ) id 1VbfvS-0001Kd-Vw; Thu, 31 Oct 2013 01:15:51 +0100 Date: Thu, 31 Oct 2013 01:15:50 +0100 Message-ID: <87zjpqz45l.wl%jch@pps.univ-paris-diderot.fr> From: Juliusz Chroboczek To: Baptiste Jonglez Subject: Re: [Babel-users] Follow-up on the new babel-rtt branch: =?ISO-8859-1?Q?=B5s?= resolution In-Reply-To: <20131030183629.GB4316@ens-lyon.fr> References: <20131030183629.GB4316@ens-lyon.fr> User-Agent: Wanderlust/2.15.9 MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (korolev.univ-paris7.fr [194.254.61.138]); Thu, 31 Oct 2013 01:15:43 +0100 (CET) X-Miltered: at korolev with ID 5271A12F.000 by Joe's j-chkmail (http : // j-chkmail dot ensmp dot fr)! X-j-chkmail-Enveloppe: 5271A12F.000 from mailhub.math.univ-paris-diderot.fr/mailhub.math.univ-paris-diderot.fr/null/mailhub.math.univ-paris-diderot.fr/ X-j-chkmail-Score: MSGID : 5271A12F.000 on korolev.univ-paris7.fr : j-chkmail score : . : R=. U=. O=. B=0.000 -> S=0.000 X-j-chkmail-Status: Ham Cc: bloat-devel , "babel-users@lists.alioth.debian.org" X-BeenThere: bloat-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: "Developers working on AQM, device drivers, and networking stacks" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 31 Oct 2013 00:15:59 -0000 Baptiste: > - Babel sees a RTT that is 400 µs higher than ping6. The babel-rtt > implementation timestamps outgoing message as late as possible, and > timestamps incoming messages as early as possible, but it's not > perfect. The good news, of course, is that the offset is pretty constant, so the samples computed by babeld are good enough to be input to the metric computation. The smoothed samples would appear to have a precision of roughly 200us, which should be good enough for almost any application. Baptiste, I'm wondering if you can count the number of Ethernet switches that way. > I'm delighted to see this measurement as collected by babel I knew you would be :-) > my sekret plan was to be able to measure heavy traffic benchmarks vs > various qdiscs like the new "fq" and older fq_codel ones... Well, the reason we decided it's worthwile to improve the precision of our measurements is that, according to Jim, you had a secret plan to use RTT to measure link-layer congestion in Wifi meshes. How many more secret plans do you have? -- Juliusz