From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753992Ab0A0Jvt (ORCPT ); Wed, 27 Jan 2010 04:51:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753820Ab0A0Jvt (ORCPT ); Wed, 27 Jan 2010 04:51:49 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:44265 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753249Ab0A0Jvs (ORCPT ); Wed, 27 Jan 2010 04:51:48 -0500 Subject: Re: [PATCH RFC tip/core/rcu] accelerate grace period if last non-dynticked CPU From: Peter Zijlstra To: Andi Kleen Cc: "Paul E. McKenney" , linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com In-Reply-To: <20100127094336.GA12522@basil.fritz.box> References: <20100125034816.GA14043@linux.vnet.ibm.com> <873a1sft9q.fsf@basil.nowhere.org> <20100127052050.GC6807@linux.vnet.ibm.com> <20100127094336.GA12522@basil.fritz.box> Content-Type: text/plain; charset="UTF-8" Date: Wed, 27 Jan 2010 10:50:50 +0100 Message-ID: <1264585850.4283.1992.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-01-27 at 10:43 +0100, Andi Kleen wrote: > > Can't you simply check that at runtime then? > > if (num_possible_cpus() > 20) > ... > > BTW the new small is large. This years high end desktop PC will come with > upto 12 CPU threads. It would likely be challenging to find a good > number for 20 that holds up with the future. If only scalability were that easy :/ These massive core/thread count things are causing more problems as well, the cpus/node ratios are constantly growing, giving grief in the page allocator as well as other places that used to scale per node. As to the current problem, the call_rcu() interface doesn't make a hard promise that the callback will be done on the same cpu, right? So why not simply move the callback list over to a more active cpu?