From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933079Ab2IFUt1 (ORCPT ); Thu, 6 Sep 2012 16:49:27 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:46760 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759654Ab2IFUtY (ORCPT ); Thu, 6 Sep 2012 16:49:24 -0400 Date: Thu, 6 Sep 2012 13:39:57 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org Subject: Re: [PATCH RFC tip/core/rcu] Add callback-free CPUs Message-ID: <20120906203957.GW2448@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120905213945.GA15216@linux.vnet.ibm.com> <1346881720.2600.48.camel@twins> <20120905234443.GY3308@linux.vnet.ibm.com> <1346926417.2600.73.camel@twins> <20120906164745.GF2448@linux.vnet.ibm.com> <1346950736.18408.43.camel@twins> <20120906174652.GM2448@linux.vnet.ibm.com> <1346955710.18408.58.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1346955710.18408.58.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12090620-9360-0000-0000-00000A4CC7FA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 06, 2012 at 08:21:50PM +0200, Peter Zijlstra wrote: > On Thu, 2012-09-06 at 10:46 -0700, Paul E. McKenney wrote: > > Getting these > > CPUs into adaptive-tick mode more quickly reduces OS jitter, which is > > one big expected benefit of adaptive-tick mode. > > I'm not sure I agree with that statement. Its a transition thing and > therefore statistically irrelevant on the whole -- assuming we > transition rarely. > > And for those who cannot deal with the transition effects, a barrier was > proposed which would wait until the system hit this state -- although > the specific implementation of this isn't clear yet afaik. > > I very much think we should focus on getting adaptive tick working as > simple as possible and worry about transition effects later, if at all. I expect that the RT folks will be interested as well, and they will likely care about the transition effects because they degrade worst-case behavior. Thanx, Paul