From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758501AbZBYRNF (ORCPT ); Wed, 25 Feb 2009 12:13:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752074AbZBYRMx (ORCPT ); Wed, 25 Feb 2009 12:12:53 -0500 Received: from e8.ny.us.ibm.com ([32.97.182.138]:42079 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751274AbZBYRMx (ORCPT ); Wed, 25 Feb 2009 12:12:53 -0500 Date: Wed, 25 Feb 2009 09:12:49 -0800 From: "Paul E. McKenney" To: Nick Piggin Cc: Ingo Molnar , linux-kernel@vger.kernel.org, vegard.nossum@gmail.com, stable@kernel.org, akpm@linux-foundation.org, penberg@cs.helsinki.fi Subject: Re: [PATCH] v4 Teach RCU that idle task is not quiscent state at boot Message-ID: <20090225171249.GD6797@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20090223161611.GA9563@linux.vnet.ibm.com> <20090223204332.GA19861@linux.vnet.ibm.com> <20090225002937.GA23733@linux.vnet.ibm.com> <20090225141945.GA28455@linux.vnet.ibm.com> <20090225160024.GB12732@elte.hu> <20090225162645.GJ22785@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090225162645.GJ22785@wotan.suse.de> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 25, 2009 at 05:26:45PM +0100, Nick Piggin wrote: > On Wed, Feb 25, 2009 at 05:00:24PM +0100, Ingo Molnar wrote: > > > > * Paul E. McKenney wrote: > > > > > +/* Internal to kernel, but needed by rcupreempt.h. */ > > > +extern int rcu_idle_cpu_truthful; > > > > The name sucks a bit ;-) 'truthful' is an emotionally laden > > statement and distracts from the technical purpose when reading > > it ;) > > > > Same for: > > > > > +extern void rcu_idle_now_means_idle(void); > > > > Also, i'm wondering, is there really no way to avoid this quirk. > > We almost got away without it for a long time. > > I wonder if you couldn't leave cpu_rq(cpu)->idle as NULL until right > up to the point where it actually becomes the "idle" thread? This > would make idle_cpu() more truthful for all other callers in early > boot code too. And rcupdate shouldn't need any changes (except the > num_online_cpus() == 1 shortcut probably remains as a nice opt). It looked to me that the idle task initialization was moved early to allow interrupt handlers to see a more normal environment, but I could easily be confused here. Thanx, Paul > > This one: > > > > > void rcu_check_callbacks(int cpu, int user) > > > { > > > if (user || > > > - (idle_cpu(cpu) && !in_softirq() && > > > - hardirq_count() <= (1 << HARDIRQ_SHIFT))) { > > > + (idle_cpu(cpu) && rcu_idle_cpu_truthful && > > > + !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) { > > > > Is a hotpath called very often ... > > > > Ingo