From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH 3/3] PM: Introduce Intel PowerClamp Driver Date: Tue, 13 Nov 2012 16:03:39 -0800 Message-ID: <20121114000339.GL2489@linux.vnet.ibm.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> <21157900.tI2QCFTxxq@vostro.rjw.lan> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e3.ny.us.ibm.com ([32.97.182.143]:44151 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756051Ab2KNAHk (ORCPT ); Tue, 13 Nov 2012 19:07:40 -0500 Received: from /spool/local by e3.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 13 Nov 2012 19:07:39 -0500 Content-Disposition: inline In-Reply-To: <21157900.tI2QCFTxxq@vostro.rjw.lan> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Rafael J. Wysocki" Cc: Arjan van de Ven , Jacob Pan , Linux PM , LKML , Rafael Wysocki , Len Brown , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , Zhang Rui , Rob Landley On Wed, Nov 14, 2012 at 12:02:00AM +0100, Rafael J. Wysocki wrote: > 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. Understood. My concern is in-kernel confusion rather than performance. Thanx, Paul