From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756851AbYIPRrw (ORCPT ); Tue, 16 Sep 2008 13:47:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751913AbYIPRrm (ORCPT ); Tue, 16 Sep 2008 13:47:42 -0400 Received: from yw-out-2324.google.com ([74.125.46.30]:60514 "EHLO yw-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752912AbYIPRrl (ORCPT ); Tue, 16 Sep 2008 13:47:41 -0400 Message-ID: <48CFF150.8070400@colorfullife.com> Date: Tue, 16 Sep 2008 19:48:00 +0200 From: Manfred Spraul User-Agent: Thunderbird 2.0.0.16 (X11/20080723) MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: linux-kernel@vger.kernel.org, cl@linux-foundation.org, mingo@elte.hu, akpm@linux-foundation.org, dipankar@in.ibm.com, josht@linux.vnet.ibm.com, schamp@sgi.com, niv@us.ibm.com, dvhltc@us.ibm.com, ego@in.ibm.com, laijs@cn.fujitsu.com, rostedt@goodmis.org, peterz@infradead.org, penberg@cs.helsinki.fi, andi@firstfloor.org Subject: Re: [PATCH, RFC] v4 scalable classic RCU implementation References: <20080821234318.GA1754@linux.vnet.ibm.com> <20080825000738.GA24339@linux.vnet.ibm.com> <20080830004935.GA28548@linux.vnet.ibm.com> <20080905152930.GA8124@linux.vnet.ibm.com> <20080915160221.GA9660@linux.vnet.ibm.com> <48CFE466.8010200@colorfullife.com> <20080916173012.GC6717@linux.vnet.ibm.com> In-Reply-To: <20080916173012.GC6717@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paul E. McKenney wrote: > >> That means an O(NR_CPUS) loop with disabled local interrupts :-( >> Is that correct? >> > > With the definition of "O()" being the worst-case execution time, yes. > But this worst case could only happen when the system was mostly idle, > in which case the added overhead should not be too horribly bad. No: "was mostly running cpu_idle()". A cpu_idle() cpu could execute lots of irqs and softirqs. So the worst case would be a system with 1 cpu/node for reserved for irq handling. The "idle" cpu would be always in no_hz mode, even though it might be 100% busy handling irqs. The remaning cpus might be 100% busy handling user space. And every quiescent state will end up in that O(NR_CPUS) loop. -- Manfred