From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758862Ab3BTIqd (ORCPT ); Wed, 20 Feb 2013 03:46:33 -0500 Received: from merlin.infradead.org ([205.233.59.134]:44141 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751280Ab3BTIqc (ORCPT ); Wed, 20 Feb 2013 03:46:32 -0500 Message-ID: <1361349985.10155.1.camel@laptop> Subject: Re: [PATCH] sched: Skip looking at skip if next or last is set From: Peter Zijlstra To: Srikar Dronamraju Cc: Ingo Molnar , LKML , Mike Galbraith Date: Wed, 20 Feb 2013 09:46:25 +0100 In-Reply-To: <20130218130146.GA7472@linux.vnet.ibm.com> References: <20130218130146.GA7472@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.2-0ubuntu0.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2013-02-18 at 18:31 +0530, Srikar Dronamraju wrote: > pick_next_entity() prefers next, then last. However code checks if the > left entity can be skipped even if next / last is set. > > Check if left entity should be skipped only if next/last is not set. You fail to explain why its a problem and continue to make a horrid mess of the code.. > Signed-off-by: Srikar Dronamraju > --- > kernel/sched/fair.c | 31 +++++++++++++++---------------- > 1 files changed, 15 insertions(+), 16 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index fdee793..cc97b12 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1900,27 +1900,26 @@ 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 next to run. If it's not unfair, run it. > */ > - if (cfs_rq->skip == se) { > - struct sched_entity *second = __pick_next_entity(se); > + if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) { > + se = cfs_rq->next; > + } else if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) { > + /* > + * Prefer last buddy, try to return the CPU to a preempted > + * task. > + */ > + se = cfs_rq->last; > + } else if (cfs_rq->skip == left) { > + /* > + * Avoid running the skip buddy, if running something else > + * can be done without getting too unfair. > + */ > + struct sched_entity *second = __pick_next_entity(left); > if (second && wakeup_preempt_entity(second, left) < 1) > se = second; > } > > - /* > - * Prefer last buddy, try to return the CPU to a preempted task. > - */ > - if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) > - se = cfs_rq->last; > - > - /* > - * Someone really wants this to run. If it's not unfair, run it. > - */ > - if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) > - se = cfs_rq->next; > - > clear_buddies(cfs_rq, se); > > return se; >