From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757598Ab0EAX1Q (ORCPT ); Sat, 1 May 2010 19:27:16 -0400 Received: from casper.infradead.org ([85.118.1.10]:52250 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752475Ab0EAX1M (ORCPT ); Sat, 1 May 2010 19:27:12 -0400 Date: Sat, 1 May 2010 16:29:17 -0700 From: Arjan van de Ven To: Pavel Machek Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mingo@elte.hu, peterz@infradead.org, tglx@linutronix.de, davej@redhat.com, cpufreq@vger.kernel.org Subject: Re: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO Message-ID: <20100501162917.06bcafed@infradead.org> In-Reply-To: <20100424045626.GA7561@elf.ucw.cz> References: <20100418115949.7b743898@infradead.org> <20100418120346.1b478410@infradead.org> <20100423052439.GB4829@ucw.cz> <20100423065248.3b0a98ab@infradead.org> <20100424045626.GA7561@elf.ucw.cz> Organization: Intel X-Mailer: Claws Mail 3.7.5 (GTK+ 2.16.6; i586-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 24 Apr 2010 06:56:26 +0200 Pavel Machek wrote: > > So... some old data. It is not exactly athlon 64 -- I don't have that > particular number for it -- but: (from my old notes): > > thinkpad x32 [52Wh] > ~~~~~~~~~~~~ > idle machine at 600MHz, min bl: 10 W > at 1.8GHz: +6.6 W > > ...so yes, I kind of see a pattern there. And you should be able to > easily see the difference, too, if you took something from that era... so I finally found a machine based on a Pentium M (similar to this Thinkpad, at least according to google) and spend half a day getting its Fedora 8 installation to compile a modern kernel (these guys don't compile very fast....). Turns out that things are not as simple as your data suggest. The complexity is in USB autosuspend. Without USB devices, I see: "powersave" 9.7 / 9.8 Watts (alternating between these readings) "ondemand" 9.7 / 9.8 Watts "performance" 9.8 Watts (solid on 9.8, not alternating) if all USB devices are in autosuspend, it's pretty much the same picture. But if there is an active USB device, the CPU will no longer go to C4, but will be stuck in C2 (this is the last generation of Intel chipsets that suffer from this behavior; "c2 popup" is what the ich4m is missing). And the C2 power behavior does show sensitivity to the CPU frequency... roughly 3 1/2 Watts for my machine. Doing the 'cat' from a usb mount as you suggested, which implies active USB DMA, shows this 3 1/2 Watts increase between the old and new ondemand. At the same time, the performance went up a little as well (a 3.7Gb took 3m32.5s before, and now takes 3m20.5s, so that saves a little of the energy back). -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org