From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751590Ab3C1EON (ORCPT ); Thu, 28 Mar 2013 00:14:13 -0400 Received: from szxga02-in.huawei.com ([119.145.14.65]:35179 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751493Ab3C1EOJ (ORCPT ); Thu, 28 Mar 2013 00:14:09 -0400 Message-ID: <5153C34B.7030708@huawei.com> Date: Thu, 28 Mar 2013 12:12:59 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130307 Thunderbird/17.0.4 MIME-Version: 1.0 To: Ingo Molnar CC: Peter Zijlstra , LKML Subject: [PATCH 5/7] cpuacct: Remove redundant NULL checks in cpuacct_charge() References: <5153C2D6.7050103@huawei.com> In-Reply-To: <5153C2D6.7050103@huawei.com> Content-Type: text/plain; charset="GB2312" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.135.68.215] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is micro optimization for the hot path. - We don't need to check if @ca is NULL in parent_ca(). - We don't need to check if @ca is NULL in the beginning of the for loop. Signed-off-by: Li Zefan --- kernel/sched/cpuacct.c | 6 +++++- kernel/sched/cpuacct.h | 2 +- 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c index 72bd971..b2aaaba 100644 --- a/kernel/sched/cpuacct.c +++ b/kernel/sched/cpuacct.c @@ -210,9 +210,13 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime) ca = task_ca(tsk); - for (; ca; ca = parent_ca(ca)) { + while (true) { u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu); *cpuusage += cputime; + + ca = parent_ca(ca); + if (!ca) + break; } rcu_read_unlock(); diff --git a/kernel/sched/cpuacct.h b/kernel/sched/cpuacct.h index bd0409b..45c1682 100644 --- a/kernel/sched/cpuacct.h +++ b/kernel/sched/cpuacct.h @@ -36,7 +36,7 @@ static inline struct cpuacct *task_ca(struct task_struct *tsk) static inline struct cpuacct *parent_ca(struct cpuacct *ca) { - if (!ca || !ca->css.cgroup->parent) + if (!ca->css.cgroup->parent) return NULL; return cgroup_ca(ca->css.cgroup->parent); } -- 1.8.0.2