Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752126Ab3CUSCv (ORCPT ); Thu, 21 Mar 2013 14:02:51 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:36594 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752100Ab3CUSCr (ORCPT ); Thu, 21 Mar 2013 14:02:47 -0400 Date: Thu, 21 Mar 2013 11:02:18 -0700 From: "Paul E. McKenney" To: Arjan van de Ven Cc: Steven Rostedt , Frederic Weisbecker , Rob Landley , linux-kernel@vger.kernel.org, josh@joshtriplett.org, zhong@linux.vnet.ibm.com, khilman@linaro.org, geoff@infradead.org, tglx@linutronix.de Subject: Re: [PATCH] nohz1: Documentation Message-ID: <20130321180218.GA3637@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1363636794.15703.32@driftwood> <20130318222548.GG3656@linux.vnet.ibm.com> <1363822338.6345.33.camel@gandalf.local.home> <20130320235545.GL3637@linux.vnet.ibm.com> <1363825631.6345.45.camel@gandalf.local.home> <514B2B03.4030301@linux.intel.com> <20130321171806.GX3637@linux.vnet.ibm.com> <514B464A.50700@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <514B464A.50700@linux.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13032118-3620-0000-0000-000001B86A4C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1930 Lines: 45 On Thu, Mar 21, 2013 at 10:41:30AM -0700, Arjan van de Ven wrote: > On 3/21/2013 10:18 AM, Paul E. McKenney wrote: > > o Use the "idle=poll" boot parameter. However, please note > > that use of this parameter can cause your CPU to overheat, > > which may cause thermal throttling to degrade your > > latencies --and that this degradation can be even worse > > than that of dyntick-idle. > > it also disables (effectively) Turbo Mode on Intel cpus... which can cost you a serious percentage of performance Thank you, added! Please see below for the updated list. Thanx, Paul ------------------------------------------------------------------------ o Dyntick-idle slows transitions to and from idle slightly. In practice, this has not been a problem except for the most aggressive real-time workloads, which have the option of disabling dyntick-idle mode, an option that most of them take. However, some workloads will no doubt want to use adaptive ticks to eliminate scheduling-clock-tick latencies. Here are some options for these workloads: a. Use PMQOS from userspace to inform the kernel of your latency requirements (preferred). b. Use the "idle=mwait" boot parameter. c. Use the "intel_idle.max_cstate=" to limit the maximum depth C-state depth. d. Use the "idle=poll" boot parameter. However, please note that use of this parameter can cause your CPU to overheat, which may cause thermal throttling to degrade your latencies -- and that this degradation can be even worse than that of dyntick-idle. Furthermore, this parameter effectively disables Turbo Mode on Intel CPUs, which can significantly reduce maximum performance. -- 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/