From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752860AbbIHGYH (ORCPT ); Tue, 8 Sep 2015 02:24:07 -0400 Received: from blu004-omc1s28.hotmail.com ([65.55.116.39]:63959 "EHLO BLU004-OMC1S28.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751392AbbIHGYE (ORCPT ); Tue, 8 Sep 2015 02:24:04 -0400 X-TMN: [5M2qLPAjZ8/0puj0166D8koO5Tu13O2j] 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> <20150908061426.GE6455@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 14:23:56 +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: <20150908061426.GE6455@byungchulpark-X58A-UD3R> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 08 Sep 2015 06:24:01.0525 (UTC) FILETIME=[F3D0B250:01D0E9FE] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/8/15 2:14 PM, Byungchul Park wrote: > On Tue, Sep 08, 2015 at 01:38:08PM +0800, Wanpeng Li wrote: >> 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 > hello, > > it is just a bug caused by not calculating a relative vruntime when > detached a task from cfs_rq, which is necessary though. Refer to Peterz's comments: | There is also a case where it was moved from fair_sched_class when it | was in a blocked state and moved back while it is running. > >>> 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. > as you may know, place_entity() is not for calculating an absolute > vruntime though.. anyway the important thing here is that, when a > sleeping task is moved back to fair class, enqueue_entity() for > DEQUEUE_SLEEP task won't be called. The enqueue_entity() for DEQUEUE_SLEEP task will be called when the task is wake up. Regards, Wanpeng Li