From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754732AbZBZIlQ (ORCPT ); Thu, 26 Feb 2009 03:41:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752469AbZBZIlA (ORCPT ); Thu, 26 Feb 2009 03:41:00 -0500 Received: from cn.fujitsu.com ([222.73.24.84]:65493 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752454AbZBZIlA (ORCPT ); Thu, 26 Feb 2009 03:41:00 -0500 Message-ID: <49A655B0.9020002@cn.fujitsu.com> Date: Thu, 26 Feb 2009 16:41:20 +0800 From: Li Zefan User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: balbir@linux.vnet.ibm.com CC: Ingo Molnar , Peter Zijlstra , Paul Menage , LKML Subject: Re: [PATCH] cpuacct: add a branch prediction References: <49A6475F.4000502@cn.fujitsu.com> <20090226083702.GI11421@balbir.in.ibm.com> In-Reply-To: <20090226083702.GI11421@balbir.in.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. ;) 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.