From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932992Ab2IFSWQ (ORCPT ); Thu, 6 Sep 2012 14:22:16 -0400 Received: from merlin.infradead.org ([205.233.59.134]:42879 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754787Ab2IFSWP convert rfc822-to-8bit (ORCPT ); Thu, 6 Sep 2012 14:22:15 -0400 Message-ID: <1346955710.18408.58.camel@twins> Subject: Re: [PATCH RFC tip/core/rcu] Add callback-free CPUs From: Peter Zijlstra To: paulmck@linux.vnet.ibm.com 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 Date: Thu, 06 Sep 2012 20:21:50 +0200 In-Reply-To: <20120906174652.GM2448@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> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.