Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932517Ab2KNC7J (ORCPT ); Tue, 13 Nov 2012 21:59:09 -0500 Received: from mga01.intel.com ([192.55.52.88]:26116 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932426Ab2KNC7I (ORCPT ); Tue, 13 Nov 2012 21:59:08 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.83,247,1352102400"; d="scan'208";a="246658915" Message-ID: <50A308FA.40001@linux.intel.com> Date: Tue, 13 Nov 2012 18:59:06 -0800 From: Arjan van de Ven User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko/20121026 Thunderbird/16.0.2 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: 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 References: <1352757831-5202-1-git-send-email-jacob.jun.pan@linux.intel.com> <1352757831-5202-4-git-send-email-jacob.jun.pan@linux.intel.com> <20121113211602.GA30150@linux.vnet.ibm.com> <20121113133922.47144a50@chromoly> <20121113222350.GH2489@linux.vnet.ibm.com> <50A2CD77.7000403@linux.intel.com> <20121114000259.GK2489@linux.vnet.ibm.com> <50A2E116.8000400@linux.intel.com> <20121113171450.3657290c@chromoly> <20121114013459.GS2489@linux.vnet.ibm.com> In-Reply-To: <20121114013459.GS2489@linux.vnet.ibm.com> X-Enigmail-Version: 1.4.5 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1545 Lines: 34 On 11/13/2012 5:34 PM, Paul E. McKenney wrote: > On Tue, Nov 13, 2012 at 05:14:50PM -0800, Jacob Pan wrote: >> On Tue, 13 Nov 2012 16:08:54 -0800 >> Arjan van de Ven wrote: >> >>>> I think I know, but I feel the need to ask anyway. Why not tell >>>> RCU about the clamping? >>> >>> I don't mind telling RCU, but what cannot happen is a bunch of CPU >>> time suddenly getting used (since that is the opposite of what is >>> needed at the specific point in time of going idle) > > Another round of RCU_FAST_NO_HZ rework, you are asking for? ;-) well we can tell you we're about to mwait and we can tell you when we're done being idle. you could just do the actual work at that point, we don't care anymore ;-) just at the start of the mandated idle period we can't afford to have more jitter than we already have (which is more than I'd like, but it's manageable. More jitter means more performance hit, since during the time of the jitter, some cpus are forced idle, e.g. costing performance, without the actual big-step power savings kicking in yet....) > If you are only having the system take 6-millisecond "vacations", probably it's not all that different from running a while (1) loop for 6 msec inside a kernel thread.... other than the power level of course... -- 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/