From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-x229.google.com (mail-wg0-x229.google.com [IPv6:2a00:1450:400c:c00::229]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id E50ED21F20F for ; Wed, 30 Oct 2013 18:23:24 -0700 (PDT) Received: by mail-wg0-f41.google.com with SMTP id b13so6746281wgh.2 for ; Wed, 30 Oct 2013 18:23:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=E/7y+1s8FBcHpk5aWnfDt+KSj8D/k1BH7S5ylyMgkZY=; b=Tuxc4AB/0Q6WoWf38mT9J3m9G3nOw5vvCm2TcGRS+91D0LaOmlsPKGCimy4/EyoN79 d963u4+jUEqsKxWY4TOP/fRVEC9NdQRzyIbwpUi5XlExt2FuL3271LR/rQW4ShA/LmMZ vcZsX015N7tglBZavEQ579IbnvEYax93TnUydzXWC+kMRagdIwW42bfoKnEKQX7WbpV4 DAaikS+spjB8yTMYxgIhPfzkActEbYsjigpWbTdQdbOy7EMJxusgb4ODpgTkCp1M0JFU mU8Ba9RfkEcyEj3xgj39JTAcMXS7x+8wva1mv1pVC4oWuaDeTJH2IsyVDR/lPFuMbMKt cLPA== MIME-Version: 1.0 X-Received: by 10.194.71.72 with SMTP id s8mr465870wju.52.1383182602509; Wed, 30 Oct 2013 18:23:22 -0700 (PDT) Received: by 10.217.67.202 with HTTP; Wed, 30 Oct 2013 18:23:22 -0700 (PDT) In-Reply-To: <87zjpqz45l.wl%jch@pps.univ-paris-diderot.fr> References: <20131030183629.GB4316@ens-lyon.fr> <87zjpqz45l.wl%jch@pps.univ-paris-diderot.fr> Date: Wed, 30 Oct 2013 18:23:22 -0700 Message-ID: Subject: =?ISO-8859-1?Q?Re=3A_=5BBabel=2Dusers=5D_Follow=2Dup_on_the_new_babel=2Drtt_bra?= =?ISO-8859-1?Q?nch=3A_=B5s_resolution?= From: Dave Taht To: Juliusz Chroboczek Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: Baptiste Jonglez , 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 01:23:25 -0000 On Wed, Oct 30, 2013 at 5:15 PM, Juliusz Chroboczek wrote: > Baptiste: > >> - Babel sees a RTT that is 400 =B5s 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. I will try to get an equivalent measurement on vastly weaker hardware (ar71xx/ath9k) on my next set of builds (after ietf), ~2 weeks. I would like measurements under various loads... > Baptiste, I'm wondering if you can count the number of Ethernet > switches that way. In cut-through mode this switch claims 400ns or so latency. http://ark.intel.com/products/76302/Intel-Ethernet-Switch-FM5224 Older models of this were better - 300ns or less. > >> 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. Yes, ~200us precision is nicely less than a txop. This will help. > How many > more secret plans do you have? One or two. ;) > -- Juliusz > > _______________________________________________ > Babel-users mailing list > Babel-users@lists.alioth.debian.org > http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/babel-users --=20 Dave T=E4ht Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.= html