Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755044Ab2KMW5m (ORCPT ); Tue, 13 Nov 2012 17:57:42 -0500 Received: from ogre.sisk.pl ([193.178.161.156]:41991 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754287Ab2KMW5k (ORCPT ); Tue, 13 Nov 2012 17:57:40 -0500 From: "Rafael J. Wysocki" To: Arjan van de Ven Cc: paulmck@linux.vnet.ibm.com, Jacob Pan , Linux PM , LKML , Rafael Wysocki , Len Brown , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , Zhang Rui , Rob Landley Subject: Re: [PATCH 3/3] PM: Introduce Intel PowerClamp Driver Date: Wed, 14 Nov 2012 00:02 +0100 Message-ID: <21157900.tI2QCFTxxq@vostro.rjw.lan> User-Agent: KMail/4.8.5 (Linux/3.7.0-rc5; KDE/4.8.5; x86_64; ; ) In-Reply-To: <50A2CD77.7000403@linux.intel.com> References: <1352757831-5202-1-git-send-email-jacob.jun.pan@linux.intel.com> <20121113222350.GH2489@linux.vnet.ibm.com> <50A2CD77.7000403@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1888 Lines: 44 On Tuesday, November 13, 2012 02:45:11 PM Arjan van de Ven wrote: > On 11/13/2012 2:23 PM, Paul E. McKenney wrote: > > On Tue, Nov 13, 2012 at 01:39:22PM -0800, Jacob Pan wrote: > >> On Tue, 13 Nov 2012 13:16:02 -0800 > >> "Paul E. McKenney" wrote: > >> > >>>> Please refer to Documentation/thermal/intel_powerclamp.txt for more > >>>> details. > >>> > >>> If I read this correctly, this forces a group of CPUs into idle for > >>> about 600 milliseconds at a time. This would indeed delay grace > >>> periods, which could easily result in user complaints. Also, given > >>> the default RCU_BOOST_DELAY of 500 milliseconds in kernels enabling > >>> RCU_BOOST, you would see needless RCU priority boosting. > >>> > >> the default idle injection duration is 6ms. we adjust the sleep > >> interval to ensure idle ratio. So the idle duration stays the same once > >> set. So would it be safe to delay grace period for this small amount in > >> exchange for less over head in each injection period? > > > > Ah, 6ms of delay is much better than 600ms. Should be OK (famous last > > words!). > > well... power clamping is not "free". > You're going to lose performance as a trade off for dropping instantaneous power consumption.... Yes. It is good to realize that when the clamping triggers, we already have some more to worry about than losing some performance. :-) The problem here is to find a way to lose as little performance as we possibly can and prevent the system from overheating at the same time. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- 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/