From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f45.google.com (mail-wg0-f45.google.com [74.125.82.45]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 310A0201AC7 for ; Thu, 3 May 2012 19:00:15 -0700 (PDT) Received: by wgbdt14 with SMTP id dt14so2018090wgb.26 for ; Thu, 03 May 2012 19:00:14 -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=/oiFroYg6ZRUmswbxAU7NWFqQPpg6kQzF+qC+DmPpGo=; b=s3LP3tnPgZ1LDoXDrTVyOhTqm7krnW9MDomH52TsW0736UlJQKHes01YQn5TjfY9Jb oxerFDgkv0M3yjM8sC3aqDtlSNze0VxuAezJ05g86Dw/EckeRzQbY2nuG/s37MXm6KQV NDvpdOM/3VT/hnmCYZkSB1QefOSX4AFinKPHutjRPYbWZQk72NplhWXjVYsqC+PnQ/SN oyl9k8iTFMITFjkWoP1DmqsBofJBpi0oGgOgK7F7YYJCzL4yXsEZIWkA/FCqzh2ZSOwC 5bHe1JnR1suzoWYrT0+wm/sYTwS608WkaAIcQ/Mo3biZ9BdX4BOKgJkaF3Dte/g9MEiZ YkCA== MIME-Version: 1.0 Received: by 10.216.141.134 with SMTP id g6mr280921wej.12.1336096813884; Thu, 03 May 2012 19:00:13 -0700 (PDT) Received: by 10.223.112.66 with HTTP; Thu, 3 May 2012 19:00:13 -0700 (PDT) In-Reply-To: <6F1038D7-AE4B-4F70-8F9B-5E99E483B5C2@gmail.com> References: <4FA3136E.3060502@pollere.com> <6F1038D7-AE4B-4F70-8F9B-5E99E483B5C2@gmail.com> Date: Thu, 3 May 2012 19:00:13 -0700 Message-ID: From: Dave Taht To: Andrew McGregor Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: codel@bufferbloat.net Subject: Re: [Codel] question about "data center" models X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 04 May 2012 02:00:17 -0000 The DCB work is on networks that run with a native RTT the width of a data center at the speed of light in the medium. Projected speed ranges are in the 100GB/sec or higher range. While there was early work on congestion control for that, it seemed to have stalled out. http://www.ieee802.org/1/pages/802.1au.html overview: (can't find a better one right now) http://www.ieee802.org/1/pages/dcbridges.html http://www.ieee802.org/1/pages/802.1az.html While there is underlying support for lossless protocols via various forms of hardware pause frames, there is an intent to run tcp over = it. On Thu, May 3, 2012 at 4:36 PM, Andrew McGregor wrot= e: > A normal configuration is more like a 300 microsecond RTT with early mark= ing RED and/or switches configured to backpressure sources with fairly shor= t queues. > > There may be enormous amounts of buffer in a switch, but it is usually di= vided among a rather large number of queues (ingress and egress queues per = port, plus perhaps several in the forwarder). > > Data center operators are very concerned about latency because in most ca= ses the metric they are tracking is the completion time of the last short f= low to complete in a transaction (that will be composed of, say, 20-odd 500= kB or thereabouts TCP connections). =A0There is often a hard time limit on = transaction components; one I've heard of is that all data for a query must= be at the aggregation node in 8ms, or it will be dropped and the query res= ult quality will go down. > > On 4/05/2012, at 11:23 AM, Kathleen Nichols wrote: > >> >> So, I thought I'd see what happens with a 1G bottleneck and a 5ms RTT. >> I'm still checking >> it out, but I thought I'd try to understand the concern. =A0So, under a >> constant heavy load, >> codel will accept a 5ms standing queue. I got the impression this was a >> concern. I'm >> not exactly certain why. How much buffer is normally in the bottleneck? >> If it's enough >> for a "nominal" RTT of 100 ms, with drop tail it will just fill up and >> stay there under >> load. So, 100ms of delay. If it's at a RTT of 5ms, then the buffer will >> fill up and give 5ms >> of delay without any ability to absorb bursts. =A0What is the normal >> configuration? >> >> =A0 =A0 =A0 Kathie >> _______________________________________________ >> Codel mailing list >> Codel@lists.bufferbloat.net >> https://lists.bufferbloat.net/listinfo/codel > > > _______________________________________________ > Codel mailing list > Codel@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/codel > --=20 Dave T=E4ht SKYPE: davetaht US Tel: 1-239-829-5608 http://www.bufferbloat.net