Return-path: Received: from rain.florz.de ([62.216.164.86]:52101 "EHLO rain.florz.dyndns.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750834AbZLUV2M (ORCPT ); Mon, 21 Dec 2009 16:28:12 -0500 Date: Mon, 21 Dec 2009 22:27:43 +0100 From: Florian Zumbiehl To: Hin-Tak Leung Cc: Andrea Merello , Larry Finger , herton@mandriva.com.br, htl10@users.sourceforge.net, linux-wireless@vger.kernel.org Subject: Re: Power consumption of RTL8187 (driver)/recommendations for low-power USB 802.11 adapter? Message-ID: <20091221212743.GB22914@florz.florz.dyndns.org> References: <20091218180205.GD2512@florz.florz.dyndns.org> <4B2BC7E3.2050907@lwfinger.net> <20091218185916.GE2512@florz.florz.dyndns.org> <4B2C100A.9000507@lwfinger.net> <20091219011306.GG2512@florz.florz.dyndns.org> <20091219184401.GH2512@florz.florz.dyndns.org> <3ace41890912191531k8703ecfr19c33f30127b2ecb@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 In-Reply-To: <3ace41890912191531k8703ecfr19c33f30127b2ecb@mail.gmail.com> Sender: linux-wireless-owner@vger.kernel.org List-ID: Hi, > > So, a base load of 3.8 W seems to be caused by any connected usb device > > preventing C3 and some 250 ms polling done by uhci_hcd, plus a bit for > > the device itself. According to > > http://www.mail-archive.com/linux-usb-users@lists.sourceforge.net/msg19354.html > > (why aren't there any message IDs on any of those archive sites, BTW?) > > that's the expected behaviour. > > Presumably power-management changes have a time granuarity i.e. if you > make the CPU busy for one moment, it would stay in the higher-power > state for a while before dropping down? That's the standard thing to > do for prevent the power state being changed too often (and have bad > effects of some sort)? Well, yeah, but: There are "only" some 1050 wakeups per second going on, 1000 of which are the timer tick, despite NO_HZ. And all of them in total seem to be using < 1 % of the CPU. Given that /proc/acpi/processor/CPU0/power lists a latency of 65 ?s for C3, I don't quite see how that fits together. Florian