From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753274AbbIHG4B (ORCPT ); Tue, 8 Sep 2015 02:56:01 -0400 Received: from blu004-omc1s30.hotmail.com ([65.55.116.41]:57573 "EHLO BLU004-OMC1S30.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751807AbbIHGz5 (ORCPT ); Tue, 8 Sep 2015 02:55:57 -0400 X-TMN: [9dzDDS8aJUHo6BTqds6wTQxMQcVDjcKM] 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: <20150908021030.GC6455@byungchulpark-X58A-UD3R> CC: Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org From: Wanpeng Li Date: Tue, 8 Sep 2015 14:55:20 +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: <20150908021030.GC6455@byungchulpark-X58A-UD3R> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 08 Sep 2015 06:55:55.0978 (UTC) FILETIME=[68EB0AA0:01D0EA03] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/8/15 10:10 AM, Byungchul Park wrote: > hello wanpeng, > > 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. > it is nothing to do with normalization. > > if vruntime - cfs_rq->min_vruntime is big even though place_entity() was > called when moved from fair class, then we actually expect that it still has > a big vruntime when moved back to fair class. > > if we don't expect that it still has a big vruntime when moved back to fair > class, we need to consider other approaches e.g. to move a position calling > place_entity() or to add place_entity() call properly .. > > however we should not touch normalization logic. in other words, if we > normalized the vruntime when leaved, then we should necessarily restore the > vruntime to a non-normalized value when moved back. Not about vruntime - cfs_rq->min_vruntime is big, I think my patch description above is confusing, and what's wrong I found is explained in the mail which reply to Peterz. > >> 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. > could you explain this in detail? when is a vruntime not normalized? > The comments in task_move_group_fair() which you removed in your commit: | * When !queued, vruntime of the task has usually NOT been normalized Regards, Wanpeng Li