From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755344AbZBZKk2 (ORCPT ); Thu, 26 Feb 2009 05:40:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753198AbZBZKkS (ORCPT ); Thu, 26 Feb 2009 05:40:18 -0500 Received: from e28smtp09.in.ibm.com ([59.145.155.9]:47943 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753111AbZBZKkR (ORCPT ); Thu, 26 Feb 2009 05:40:17 -0500 Date: Thu, 26 Feb 2009 16:10:08 +0530 From: Balbir Singh To: Li Zefan Cc: Ingo Molnar , Peter Zijlstra , Paul Menage , LKML Subject: Re: [PATCH] cpuacct: add a branch prediction Message-ID: <20090226104008.GJ11421@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <49A6475F.4000502@cn.fujitsu.com> <20090226083702.GI11421@balbir.in.ibm.com> <49A655B0.9020002@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <49A655B0.9020002@cn.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Li Zefan [2009-02-26 16:41:20]: > Balbir Singh wrote: > > * Li Zefan [2009-02-26 15:40:15]: > > > >> cpuacct_charge() is in fast-path, and checking of !cpuacct_susys.active > >> always returns false after cpuacct has been initialized at system boot. > >> > >> Signed-off-by: Li Zefan > >> --- > >> kernel/sched.c | 2 +- > >> 1 files changed, 1 insertions(+), 1 deletions(-) > >> > >> diff --git a/kernel/sched.c b/kernel/sched.c > >> index 410eec4..fd2f7fc 100644 > >> --- a/kernel/sched.c > >> +++ b/kernel/sched.c > >> @@ -9589,7 +9589,7 @@ static void cpuacct_charge(struct task_struct *tsk, u64 cputime) > >> struct cpuacct *ca; > >> int cpu; > >> > >> - if (!cpuacct_subsys.active) > >> + if (unlikely(!cpuacct_subsys.active)) > > > > What happens if most distros make cpuacct_subsys active? Can we decide > > on unlikely depending on how the system is configured? > > > > Note, it's ->active but not ->disabled. ;) > I've seen that > And note, I make it "unlikely(!cpuacct_subsys.active)", but not "unlikely(cpuacct_subsys.active)" > > ->active can't be configured by users. If CONFIG_CGROUP_CPUACCT is enabled, > cpuacct_subsys.active will be set to true after cpuacct is initialized. > My point is the likely/unlikely in this case depends on turning on/off CONFIG_CGROUP_CPUACCT? Am I missing something? -- Balbir