From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-33-ewr.dyndns.com (mxout-075-ewr.mailhop.org [216.146.33.75]) by lists.bufferbloat.net (Postfix) with ESMTP id AD34A2E0271 for ; Tue, 15 Mar 2011 14:02:41 -0700 (PDT) Received: from scan-31-ewr.mailhop.org (scan-31-ewr.local [10.0.141.237]) by mail-33-ewr.dyndns.com (Postfix) with ESMTP id A98706F8786 for ; Tue, 15 Mar 2011 21:02:40 +0000 (UTC) X-Spam-Score: 0.0 () X-Mail-Handler: MailHop by DynDNS X-Originating-IP: 70.61.120.58 Received: from smtp.tuxdriver.com (charlotte.tuxdriver.com [70.61.120.58]) by mail-33-ewr.dyndns.com (Postfix) with ESMTP id 20D7B6F8236 for ; Tue, 15 Mar 2011 21:02:35 +0000 (UTC) Received: from uucp by smtp.tuxdriver.com with local-rmail (Exim 4.63) (envelope-from ) id 1PzbMP-0006g7-Py; Tue, 15 Mar 2011 17:00:57 -0400 Received: from linville-8530p.local (linville-8530p.local [127.0.0.1]) by linville-8530p.local (8.14.4/8.14.4) with ESMTP id p2FKpmfG026726; Tue, 15 Mar 2011 16:51:48 -0400 Received: (from linville@localhost) by linville-8530p.local (8.14.4/8.14.4/Submit) id p2FKple8026724; Tue, 15 Mar 2011 16:51:47 -0400 Date: Tue, 15 Mar 2011 16:51:47 -0400 From: "John W. Linville" To: Jonathan Morton Message-ID: <20110315205146.GF2542@tuxdriver.com> References: <4D7F4121.40307@freedesktop.org> <20110315175942.GA10064@goldfish> <1300212877.2087.2155.camel@tardy> <20110315183111.GB2542@tuxdriver.com> <29B06777-CC5F-4802-8727-B04F58CDA9E3@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <29B06777-CC5F-4802-8727-B04F58CDA9E3@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) 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 21:02:42 -0000 On Tue, Mar 15, 2011 at 09:40:06PM +0200, Jonathan Morton wrote: > > On 15 Mar, 2011, at 8:31 pm, John W. Linville wrote: > > > If you don't throttle _both_ > > the _enqueue_ and the _dequeue_, then you could be keeping a nice, > > near-empty tx queue on the host and still have a long, bloated queue > > building at the device. > > Don't devices at least let you query how full their queue is? I suppose it depends on what you mean? Presumably drivers know that, or at least can figure it out. The accuracy of that might depend on the exact mechanism, how often the tx rings are replinished, etc. However, I'm not aware of any API that would let something in the stack (e.g. a qdisc) query the device driver for the current device queue depth. At least, I don't think Linux has one -- do other kernels/stacks provide that? John -- John W. Linville Someday the world will need a hero, and you linville@tuxdriver.com might be all we have. Be ready.