From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-x230.google.com (mail-we0-x230.google.com [IPv6:2a00:1450:400c:c03::230]) (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 07A9321F1EC for ; Mon, 24 Mar 2014 10:09:57 -0700 (PDT) Received: by mail-we0-f176.google.com with SMTP id x48so3636636wes.35 for ; Mon, 24 Mar 2014 10:09:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:date:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=pM9NnnfIzac+OWjRgTqY57/+dhP1C+NdxZorLmGNFe8=; b=osx31GIpUM5+KHeRL/GgeUS4rAxiuIeLd7bavV2QgVAGcBnm5R2epT3f+m+77cOzdA hIFZEpBvr2amDx5SasmoBNU/wF2NiPFsICLql0v/Ap5g2n+fElwBLdZlhGctsYf4ryPi kjHpcOTAoDOry+LFgyVUv8e5WCRkXUNsUG6mbWw0cLmsn15Cqqwy+XjxSOR+AB2gT0NG BPoV842cg6r2O7KjvWwxce+Y7zjBdD7ZSuPN9M1YF/Rgoe5zaWn3x7SgqpAU3d2D57xT duvRQKn4hn21DRVkuxQmYcNg0NxeELyoR3D47sMX71Mev54TFM1FS2g7d3TKgm31T7G9 YXUA== MIME-Version: 1.0 X-Received: by 10.180.97.37 with SMTP id dx5mr16046994wib.53.1395680995954; Mon, 24 Mar 2014 10:09:55 -0700 (PDT) Received: by 10.216.8.1 with HTTP; Mon, 24 Mar 2014 10:09:55 -0700 (PDT) Date: Mon, 24 Mar 2014 10:09:55 -0700 Message-ID: From: Dave Taht To: Eric Dumazet Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: "Steinar H. Gunderson" , bloat Subject: [Bloat] Replacing pfifo_fast? (and using sch_fq + hystart fixes) X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 24 Mar 2014 17:09:58 -0000 As this thread has forked considerably from "AQM STILL not making it into l2 equipment", forking it... On Sun, Mar 23, 2014 at 12:27 PM, Eric Dumazet wro= te: > On Fri, 2014-03-21 at 22:13 +0000, Dave Taht wrote: > >> Are you ready to make sch_fq the default in 3.15? > > > sch_fq depends on ktime_get(), so it is a no go if you have > clocksource using hpet. pfifo_fast doesn't have such issues. It has long been my hope that conventional distros would start selecting sch_fq and sch_fq_codel up in safe scenarios. 1) Can an appropriate clocksource be detected from userspace? if [ have_good_clocksources ] then if [ i am a router ] then sysctl -w something=3Dfq_codel # or is it an entry in proc? else sysctl -w something=3Dsch_fq fi fi How early in boot would this have to be to take effect? 2) In the case of a server machine providing vms, and meeting the above precondition(s), what would be a more right qdisc, sch_fq or sch_codel? 3) Containers? 4) The machine in the vm going through the virtual ethernet interface? (I don't understand to what extent tracking the exit of packets from tcp th= rough the stack and vm happens - I imagine a TSO is preserved all the way through= , and also imagine that tcp small queues doesn't survive transit through the = vm, but I am known to have a fevered imagination. > Another issue is TCP CUBIC Hystart 'ACK TRAIN' detection that triggers > early, since goal of TSO autosizing + FQ/pacing is to get ACK clocking > every ms. By design, it tends to get ACK trains, way before the cwnd > might reach BDP. Fascinating! Push on one thing, break another. As best I recall hystart had= a string of issues like this in it's early deployment. /me looks forward to one day escaping 3.10-land and observing this for hims= elf so some sort of bidirectional awareness of the underlying qdisc would be ne= eded to retune hystart properly. Is ms resolution the best possible at this point? > > > --=20 Dave T=E4ht Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.= html