Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757310AbXL3Om1 (ORCPT ); Sun, 30 Dec 2007 09:42:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752911AbXL3OmU (ORCPT ); Sun, 30 Dec 2007 09:42:20 -0500 Received: from cantor2.suse.de ([195.135.220.15]:45737 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752323AbXL3OmT (ORCPT ); Sun, 30 Dec 2007 09:42:19 -0500 To: Eduard-Gabriel Munteanu Cc: pharon@gmail.com, Rene Herman , "David P. Reed" , Richard Harman , LKML , Ingo Molnar Subject: Re: [PATCH] Option to disable AMD C1E (allows dynticks to work) From: Andi Kleen References: <47765D11.2040903@reed.com> <1198967334.5049.3.camel@iamer-laptop> <4776F6A0.9010801@keyaccess.nl> <1198979361.11150.2.camel@iamer-laptop> <20071230121725.11d05099@linux360.ro> Date: Sun, 30 Dec 2007 15:42:17 +0100 In-Reply-To: <20071230121725.11d05099@linux360.ro> (Eduard-Gabriel Munteanu's message of "Sun\, 30 Dec 2007 12\:17\:25 +0200") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2089 Lines: 47 Eduard-Gabriel Munteanu writes: > > Other kernel developers, as discussed previously in this thread, are > working on a HPET-driven dynticks (as opposed to the current > LAPIC-driven one), but the change isn't that easy to make. No, actually HPET based dyntick has been implemented for a long time (as long as APIC based dyntick). APIC based dyntick is preferred because it is a little cheaper, but both are there. The problem is just that many BIOSes don't tell the kernel about the HPET location (even when the chipset supports it) because that wasn't needed for older Windows versions. And without the BIOS telling the kernel HPET it doesn't know where it is and can't use it when the APIC timer is not usable. The ongoing work is to implement hpet=force code that knows about various chipsets and reads their hardware registers directly and then uses the HPET timer without BIOS support. The reason it is still an option is that there used to be at least one old chipset where forcing the HPET could trigger hardware bugs. On the other hand it is expected that BIOS versions support Vista also supply HPET, so that problem will hopefully get better. > This way, > dynticks and C1E could be both enabled and thus save more power. I would not expect too much over a HZ=100 kernel on current AMD. C1e doesn't have too much latency on its own. iirc at least on current AMD platforms sleeping for longer didn't make too much difference. With HZ=250 it might be borderline, but I would not expect miracles. It's probably only clearly a good idea if you're on a HZ=1000 kernel or have applications that need very precise hrtimers (but that might cost more power again because it'll cause more wakeups) Of course this can always change in future systems -- these are just rules of thumb currently. -Andi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/