From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-12-ewr.dyndns.com (mxout-116-ewr.mailhop.org [216.146.33.116]) by lists.bufferbloat.net (Postfix) with ESMTP id 95E732E0271 for ; Tue, 15 Mar 2011 15:26:32 -0700 (PDT) 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 4D08D931E09 for ; Tue, 15 Mar 2011 22:26:31 +0000 (UTC) X-Spam-Score: -1.0 (-) X-Mail-Handler: MailHop by DynDNS X-Originating-IP: 74.125.82.47 Received: from mail-ww0-f47.google.com (mail-ww0-f47.google.com [74.125.82.47]) by mail-12-ewr.dyndns.com (Postfix) with ESMTP id E0220931E06 for ; Tue, 15 Mar 2011 22:26:30 +0000 (UTC) Received: by wwk4 with SMTP id 4so1144789wwk.28 for ; Tue, 15 Mar 2011 15:26:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:subject:mime-version:content-type:from :in-reply-to:date:cc:content-transfer-encoding:message-id:references :to:x-mailer; bh=+azkZDGMgAF2oGw0DKIl52l8WqjToPDVpYjdO5pIjLI=; b=oEdrdSQmPlKJE7Rl5pnRDU2M9pBlfbk8NPP4Fc7GfSF7kaHqIFwt5cs4yQTD+07Bxv 4RM5+meXlZ0WDor5xyxU5TrvNyRzZg/jPkuVcSm3dgDylR0xb55ZlWtgMdBrHQhqui2w jZnk6oai5MxGVLReoDm6r3QxO1DhS00UU3CEU= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:mime-version:content-type:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to:x-mailer; b=AXO3oQkTZNDAiESmOwj+5+hJ0K9VnhRm9do7sorw8NSnqkRBLa4kviW6CNI5t4uW5C rso6JDdaqCNwfGd/iGFny1uL0GmTMdDsGuXMLLQ/vg93yFnPK6PVsavUH4moj6Szmgzo m7d5hhatLV6XzjjGyYhsY8SfcMjyWaBc07c/E= Received: by 10.227.1.151 with SMTP id 23mr11879wbf.175.1300227990125; Tue, 15 Mar 2011 15:26:30 -0700 (PDT) Received: from [192.168.239.42] (xdsl-83-150-84-172.nebulazone.fi [83.150.84.172]) by mx.google.com with ESMTPS id x1sm287562wbh.14.2011.03.15.15.26.29 (version=TLSv1/SSLv3 cipher=OTHER); Tue, 15 Mar 2011 15:26:29 -0700 (PDT) Mime-Version: 1.0 (Apple Message framework v1082) Content-Type: text/plain; charset=us-ascii From: Jonathan Morton In-Reply-To: <20110315151946.31e86b46@nehalam> Date: Wed, 16 Mar 2011 00:26:27 +0200 Content-Transfer-Encoding: quoted-printable Message-Id: References: <4D7F4121.40307@freedesktop.org> <20110315175942.GA10064@goldfish> <1300212877.2087.2155.camel@tardy> <20110315183111.GB2542@tuxdriver.com> <29B06777-CC5F-4802-8727-B04F58CDA9E3@gmail.com> <20110315205146.GF2542@tuxdriver.com> <219C7840-ED79-49EA-929D-96C5A6200401@gmail.com> <20110315151946.31e86b46@nehalam> To: Stephen Hemminger X-Mailer: Apple Mail (2.1082) Cc: bloat@lists.bufferbloat.net Subject: Re: [Bloat] Random idea in reaction to all the discussion of TCP flavours - timestamps? 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: Tue, 15 Mar 2011 22:26:33 -0000 On 16 Mar, 2011, at 12:19 am, Stephen Hemminger wrote: >> Knowing the occupancy of the hardware buffer is useful if the size of = the buffer cannot be changed, because it is then possible to simply = decline to fill the buffer more than a certain amount. If you can also = assume that packets are sent in order of submission, or by some other = easy rule, then you can also infer the time that the oldest packet has = spent there, and use it to tune the future occupancy limit even if you = can't cancel the old packet. >>=20 >> Cancelling old packets is potentially desirable because it allows = TCPs and applications to retransmit (which they will do anyway) without = fear of exacerbating a wireless congestion collapse. I do appreciate = that not all hardware will support this, however, and it should be = totally unnecessary for wired links. >=20 > Have you looked at actual hardware interfaces. They usually are = designed to > be "fire and go" with little to no checking by CPU. This is = intentional because > of the overhead of bus and CPU access. Once packets go into the tx = ring there > is no choice but to send or shutdown the device. For a wired device that would certainly make sense. For a wireless = device some extra flexibility is plausible, even if it doesn't exist in = practice. - Jonathan