Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751897Ab2KMVja (ORCPT ); Tue, 13 Nov 2012 16:39:30 -0500 Received: from mga14.intel.com ([143.182.124.37]:25177 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751353Ab2KMVj3 (ORCPT ); Tue, 13 Nov 2012 16:39:29 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.83,768,1352102400"; d="scan'208";a="167988873" Date: Tue, 13 Nov 2012 13:39:22 -0800 From: Jacob Pan To: paulmck@linux.vnet.ibm.com Cc: Linux PM , LKML , Rafael Wysocki , Len Brown , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , Zhang Rui , Rob Landley , Arjan van de Ven Subject: Re: [PATCH 3/3] PM: Introduce Intel PowerClamp Driver Message-ID: <20121113133922.47144a50@chromoly> In-Reply-To: <20121113211602.GA30150@linux.vnet.ibm.com> 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> Organization: OTC X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1810 Lines: 43 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? > Of course, if the idle period extended for longer, you would see RCU > CPU stall warnings. And if the idle period extended indefinitely, you > could hang the system -- the RCU callbacks on the idled CPU could not > be invoked, and if one of those RCU callbacks was waking someone up, > that someone would not be woken up. > for the same algorithm, idle duration is not extended. the injected idle loop also yield to pending softirqs, i guess that is what rcu callbacks are using? > It looks like you could end up with part of the system powerclamped > in some situations, and with all of it powerclamped in other > situations. Is that the case, or am I confused? > could you explain the part that is partially powerclamped? > Thanx, Paul [Jacob Pan] -- Thanks, Jacob -- 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/