From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-12-ewr.dyndns.com (mxout-151-ewr.mailhop.org [216.146.33.151]) by lists.bufferbloat.net (Postfix) with ESMTP id 39CD62E067C for ; Fri, 4 Feb 2011 10:43:37 -0800 (PST) Received: from scan-11-ewr.mailhop.org (scan-11-ewr.local [10.0.141.229]) by mail-12-ewr.dyndns.com (Postfix) with ESMTP id 5C780931640 for ; Fri, 4 Feb 2011 18:43:36 +0000 (UTC) X-Spam-Score: 0.1 () X-Mail-Handler: MailHop by DynDNS X-Originating-IP: 75.145.127.229 Received: from gw.co.teklibre.org (75-145-127-229-Colorado.hfc.comcastbusiness.net [75.145.127.229]) by mail-12-ewr.dyndns.com (Postfix) with ESMTP id 869EF930D68 for ; Fri, 4 Feb 2011 18:43:34 +0000 (UTC) Received: from cruithne.co.teklibre.org (unknown [IPv6:2002:4b91:7fe5:2:21c:25ff:fe80:46f9]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "cruithne.co.teklibre.org", Issuer "CA Cert Signing Authority" (verified OK)) by gw.co.teklibre.org (Postfix) with ESMTPS id 43DAD5E88A for ; Fri, 4 Feb 2011 11:43:32 -0700 (MST) Received: by cruithne.co.teklibre.org (Postfix, from userid 1000) id 8FB6F121B77; Fri, 4 Feb 2011 11:43:30 -0700 (MST) From: d@taht.net (Dave =?utf-8?Q?T=C3=A4ht?=) To: Juliusz Chroboczek Organization: Teklibre - http://www.teklibre.com References: <87k4hgdte9.fsf@trurl.pps.jussieu.fr> <4D4C05A3.3000901@freedesktop.org> <871v3nemck.fsf_-_@trurl.pps.jussieu.fr> Date: Fri, 04 Feb 2011 11:43:30 -0700 In-Reply-To: <871v3nemck.fsf_-_@trurl.pps.jussieu.fr> (Juliusz Chroboczek's message of "Fri, 04 Feb 2011 18:33:15 +0100") Message-ID: <87r5bnmyi5.fsf@cruithne.co.teklibre.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: bloat@lists.bufferbloat.net Subject: Re: [Bloat] Buffer bloat at the sender 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: Fri, 04 Feb 2011 18:43:39 -0000 Juliusz Chroboczek writes: >> Juliusz, have you thought about the host case at all? > >> One of the places we're getting insane buffering is in the operating >> systems themselves (e.g. the experiment I did with a 100Mbps >> switch). > > Yes. You have three to four layers of buffering: > > (1) the device driver's buffer; > (2) the packet scheduler's buffer; > (3) TCP's buffer; > (4) the application's buffer. > > It will come as no surprise to the readers of this list that (1) and (2) > are usually too large. For example, (1) the ath9k driver has a buffer > of 200 packets; and (2) the default scheduler queue is 1000 packets (!). The ath9k driver I have has 512 buffers, organized into 10 queues of various usages that I don't think are actually being used for much (need a way to gain insight into the queue usage and qdisc interaction), with TX_RETRIES set to 13. Fairly current openwrt head. I've put a patch out there to reduce this to (I think) effectively a queue depth of 3, retries of 4, throughout, and the results are thus far amazing. > >> My intuition is that we have to do AQM in hosts, not just routers. > > Hmm... I would argue that the sending host is somewhat easier than the > intermediate router. In the sender, the driver/packet scheduler can > apply backpressure to the transport layer, to cause it to slow down > without the need for the lengthy feedback loop that dropping/delaying > a packet in an intermediate router has to rely on [1]. > > Unfortunately, at least under Linux, most drivers do not apply > backpressure correctly. Markus Kittenberger has recently determined [2] > that among b43-legacy, ath5k, ath9k and madwifi, only the former two do > the right thing. I was wondering about madwifi in the context of the mesh potato. Thank you. I have been looking over the mq qdisc, it's not clear how well it's being used. > > --Juliusz > > [1] Now why did we give up on source quench again? > [2] http://article.gmane.org/gmane.network.olsr.user/4264 > _______________________________________________ > Bloat mailing list > Bloat@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/bloat -- Dave Taht http://nex-6.taht.net