From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: [linux-pm] power draw depending on PHY speed Date: Fri, 28 Aug 2009 20:29:07 +0100 Message-ID: <1251487747.2785.13.camel@achroite> References: <76FA3B279DD9DA48896E2B40494495720368E449@USA7061MS02.na.xerox.net> <200908282103.59159.rjw@sisk.pl> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: "Leisner, Martin" , linux-pm@lists.linux-foundation.org, martyleisner@yahoo.com, NetDEV list To: "Rafael J. Wysocki" Return-path: Received: from smarthost02.mail.zen.net.uk ([212.23.3.141]:39199 "EHLO smarthost02.mail.zen.net.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752316AbZH1T3M (ORCPT ); Fri, 28 Aug 2009 15:29:12 -0400 In-Reply-To: <200908282103.59159.rjw@sisk.pl> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, 2009-08-28 at 21:03 +0200, Rafael J. Wysocki wrote: > On Friday 28 August 2009, Leisner, Martin wrote: > > While doing some current probe measurements (i.e. to measure the effects > > of NAP and frequency scaling with a freescale processor) I noticed some > > very > > significant differents if we ran on 100Mbit of 1000Mbit ethernet. > > > > The hardware guys like at their data sheets and agreed. > > > > Does anyone "drop ethernet speed" to save power? > > (when a system is idle, is isn't necessary to run 1G ethernet). > > I don't know, really. This is a netdev question IMO (CC added). Doing this through the existing autonegotiation mechanism is a bad idea, because it requires bringing the link down, possibly for a few seconds. There is a standard on the way (802.3az, aka Energy-Efficient Ethernet or EEE) which will allow for speed renegotiation without dropping the link. > > When a system has WOL capability, what speed does it run at when the > > system is sleeping? > > That's a very good question. I bet that depends on the NIC in question, at > least I'm not sure if any spec regulates it. I'm not aware of a spec, but generally a 1G or 10G multi-speed PHY will not advertise speeds higher than 100 Mbit/s when sleeping. Ben. -- Ben Hutchings, Senior Software Engineer, Solarflare Communications Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.