From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752202AbbIHDqM (ORCPT ); Mon, 7 Sep 2015 23:46:12 -0400 Received: from blu004-omc1s13.hotmail.com ([65.55.116.24]:59949 "EHLO BLU004-OMC1S13.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751197AbbIHDqJ (ORCPT ); Mon, 7 Sep 2015 23:46:09 -0400 X-TMN: [gf4ghXl0iDcXkPiGkLYTj1KwtSL05Wt9] X-Originating-Email: [wanpeng.li@hotmail.com] Message-ID: Subject: Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair() To: Peter Zijlstra References: <20150907140221.GZ3644@twins.programming.kicks-ass.net> CC: Ingo Molnar , linux-kernel@vger.kernel.org, byungchul.park@lge.com, yuyang.du@intel.com From: Wanpeng Li Date: Tue, 8 Sep 2015 11:46:01 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20150907140221.GZ3644@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 08 Sep 2015 03:46:07.0004 (UTC) FILETIME=[E48F85C0:01D0E9E8] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/7/15 10:02 PM, Peter Zijlstra wrote: > Please always Cc at least the person who wrote the lines you modify. > > On Mon, Sep 07, 2015 at 05:45:20PM +0800, Wanpeng Li wrote: >> The sleeper task will be normalized when moved from fair_sched_class, in >> order that vruntime will be adjusted either the task is running or sleeping >> when moved back. The nomalization in switch_to_fair for sleep task will >> result in lose fair sleeper bonus in place_entity() once the vruntime - >> cfs_rq->min_vruntime is big when moved from fair_sched_class. >> >> This patch fix it by adjusting vruntime just during migrating as original >> codes since the vruntime of the task has usually NOT been normalized in >> this case. > Sorry, I cannot follow that at all. Maybe its me being sleep deprived, > but could you try that again? When changing away from the fair class while sleeping, relative vruntime is calculated to handle the case sleep when moved from fair_sched_class and running when moved to fair_sched_class. The absolute vruntime will be calculated in enqueue_entity() either the task is running or sleeping when moved back. The fair sleeper bonus should be gained in place_entity() if the task is still sleeping. However, after recent commit ( 23ec30ddd7c1306: 'sched: add two functions for att(det)aching a task to(from) a cfs_rq'), the absolute vruntime will be calculated in switched_to_fair(), so the max_vruntime() which is called in place_entity() will select the absolute vruntime which is calculated in switched_to_fair() as the se->vruntime and lose the fair sleeper bonus. Regards, Wanpeng Li > >> Signed-off-by: Wanpeng Li >> --- >> kernel/sched/fair.c | 11 +++++++---- >> 1 files changed, 7 insertions(+), 4 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index d26d3b7..eb9aa35 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -8005,9 +8005,6 @@ static void attach_task_cfs_rq(struct task_struct *p) >> >> /* Synchronize task with its cfs_rq */ >> attach_entity_load_avg(cfs_rq, se); >> - >> - if (!vruntime_normalized(p)) >> - se->vruntime += cfs_rq->min_vruntime; >> } >> >> static void switched_from_fair(struct rq *rq, struct task_struct *p) >> @@ -8066,14 +8063,20 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) >> #ifdef CONFIG_FAIR_GROUP_SCHED >> static void task_move_group_fair(struct task_struct *p) >> { >> + struct sched_entity *se = &p->se; >> + struct cfs_rq *cfs_rq = cfs_rq_of(se); >> + >> detach_task_cfs_rq(p); >> set_task_rq(p, task_cpu(p)); >> >> #ifdef CONFIG_SMP >> /* Tell se's cfs_rq has been changed -- migrated */ >> - p->se.avg.last_update_time = 0; >> + se->avg.last_update_time = 0; >> #endif >> attach_task_cfs_rq(p); >> + >> + if (!vruntime_normalized(p)) >> + se->vruntime += cfs_rq->min_vruntime; >> } >> >> void free_fair_sched_group(struct task_group *tg) >> -- >> 1.7.1 >>