From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752409AbbIHFia (ORCPT ); Tue, 8 Sep 2015 01:38:30 -0400 Received: from blu004-omc1s35.hotmail.com ([65.55.116.46]:65389 "EHLO BLU004-OMC1S35.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751428AbbIHFiS (ORCPT ); Tue, 8 Sep 2015 01:38:18 -0400 X-TMN: [j9AMpv2D67ohI6eN/aVYgBLQc3yOqot8] X-Originating-Email: [wanpeng.li@hotmail.com] Message-ID: Subject: Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair() To: Byungchul Park References: <20150907140221.GZ3644@twins.programming.kicks-ass.net> <20150908052817.GD6455@byungchulpark-X58A-UD3R> CC: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, yuyang.du@intel.com From: Wanpeng Li Date: Tue, 8 Sep 2015 13:38:08 +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: <20150908052817.GD6455@byungchulpark-X58A-UD3R> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 08 Sep 2015 05:38:16.0451 (UTC) FILETIME=[8F9FA530:01D0E9F8] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/8/15 1:28 PM, Byungchul Park wrote: > On Tue, Sep 08, 2015 at 11:46:01AM +0800, Wanpeng Li wrote: >> 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 > i don't think relative vruntime is calculated to handle the special case > you mentioned. i think the calculation is necessary for all cases detaching Please refer why the relative vruntime caculation is introduced to switched_from_fair(): https://lkml.org/lkml/2011/1/17/129 > a task from a cfs_rq. > >> absolute vruntime will be calculated in enqueue_entity() either the >> task is running or sleeping when moved back. The fair sleeper bonus > i think absolute vruntime is calculated in enqueue_entuty() only when the > task is on rq. therefore in the case that the task is not on rq, > switched_to_fair() has to calculate the absolute vruntime instread. Absolute vruntime is caculated in place_entity() which is called by enqueue_entity() for DEQUEUE_SLEEP task. Regards, Wanpeng Li > >> 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. > please refer my another reply, and let me know if i missed something. > > thanks, > byungchul > >> 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 >>>> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/