From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751314Ab2AQCgk (ORCPT ); Mon, 16 Jan 2012 21:36:40 -0500 Received: from e28smtp04.in.ibm.com ([122.248.162.4]:54648 "EHLO e28smtp04.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750769Ab2AQCgj (ORCPT ); Mon, 16 Jan 2012 21:36:39 -0500 Message-ID: <4F14DEAE.60702@linux.vnet.ibm.com> Date: Tue, 17 Jan 2012 10:36:30 +0800 From: Michael Wang User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.24) Gecko/20111108 Thunderbird/3.1.16 MIME-Version: 1.0 To: Peter Zijlstra CC: ingo Molnar , LKML Subject: [PATCH v2] sched: Accelerate "pick_next_entity" under special condition References: <4F13EFBE.1030002@linux.vnet.ibm.com> <1326707503.2442.219.camel@twins> In-Reply-To: <1326707503.2442.219.camel@twins> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit x-cbid: 12011702-5564-0000-0000-000000F99C0C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: wangyun In original code, we get the next entity in this way: if(condition1) result=value1; if(condition2) result=value2; if(condition3) result=value3; return result; So if condition3 is true, we will get value3, but still need to check condition1 and condition2, this will waste our time. This patch will change the way like: if(condition3) { result=value3; goto out; } if(condition2) { result=value2; goto out; } if(condition1) { result=value1; goto out; } out: return result; So we can avoid check condition2 and condition1 when condition3 is true now. v2: 1. do not use ugly macro any more. 2. add more description. Signed-off-by: Michael Wang --- kernel/sched/fair.c | 26 +++++++++++++++----------- 1 files changed, 15 insertions(+), 11 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 84adb2d..e8a72b2 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1308,29 +1308,33 @@ static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq) struct sched_entity *left = se; /* - * Avoid running the skip buddy, if running something else can - * be done without getting too unfair. + * Someone really wants this to run. If it's not unfair, run it. */ - if (cfs_rq->skip == se) { - struct sched_entity *second = __pick_next_entity(se); - if (second && wakeup_preempt_entity(second, left) < 1) - se = second; + if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) { + se = cfs_rq->next; + goto out; } /* * Prefer last buddy, try to return the CPU to a preempted task. */ - if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) + if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) { se = cfs_rq->last; + goto out; + } /* - * Someone really wants this to run. If it's not unfair, run it. + * Avoid running the skip buddy, if running something else can + * be done without getting too unfair. */ - if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) - se = cfs_rq->next; + if (cfs_rq->skip == se) { + struct sched_entity *second = __pick_next_entity(se); + if (second && wakeup_preempt_entity(second, left) < 1) + se = second; + } +out: clear_buddies(cfs_rq, se); - return se; } -- 1.7.4.1