From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932255AbcHWPkU (ORCPT ); Tue, 23 Aug 2016 11:40:20 -0400 Received: from foss.arm.com ([217.140.101.70]:38473 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754467AbcHWPkR (ORCPT ); Tue, 23 Aug 2016 11:40:17 -0400 Subject: Re: [PATCH v1 00/10] Optimize sched avgs computation and implement flat util hierarchy To: Vincent Guittot , Peter Zijlstra References: <1470788095-2125-1-git-send-email-yuyang.du@intel.com> <20160810002352.GB3273@intel.com> <20160822232637.GC3273@intel.com> <20160823141341.GP10153@twins.programming.kicks-ass.net> Cc: Yuyang Du , Ingo Molnar , linux-kernel , Benjamin Segall , Paul Turner , Morten Rasmussen , Matt Fleming , Mike Galbraith From: Dietmar Eggemann Message-ID: <474c486c-84b3-14b0-6861-336a129f7ed8@arm.com> Date: Tue, 23 Aug 2016 16:39:51 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/08/16 15:45, Vincent Guittot wrote: > On 23 August 2016 at 16:13, Peter Zijlstra wrote: >> On Tue, Aug 23, 2016 at 03:28:19PM +0200, Vincent Guittot wrote: >>> I still wonder if using a flat util hierarchy is the right solution to >>> solve this problem with utilization and task group. I have noticed >>> exact same issues with load that generates weird task placement >>> decision and i think that we should probably try to solve both wrong >>> behavior with same mechanism. but this is not possible with flat >>> hierarchy for load >>> >>> Let me take an example. >>> TA is a always running task on CPU1 in group /root/level1/ >>> TB wakes up on CPU0 and moves TA into group /root/level2/ >>> Even if TA stays on CPU1, runnable_load_avg of CPU1 root cfs rq will become 0. >> >> Because while we migrate the load_avg on /root/level2, we do not >> propagate the load_avg up the hierarchy? > > yes. At now, the load of a cfs_rq and the load of its sched_entity > that represents it at parent level are disconnected I guess you say 'disconnected' because cfs_rq and se (w/ cfs_rq eq. se->my_q) are now independent pelt signals where as before the rewrite they were 'connected' for load via __update_tg_runnable_avg(), __update_group_entity_contrib() in __update_entity_load_avg_contrib() and for utilization via 'se->avg.utilization_avg_contrib = group_cfs_rq(se)->utilization_load_avg' in __update_entity_utilization_avg_contrib(). IMHO, there was also this 'connection' between se and cfs_rq (w/ se->cfs_rq eq. cfs_rq) in update_entity_load_avg(, update_cfs_rq = 1) which guaranteed that the change in the se was immediately visible on the cfs_rq representing the parent task group. if (se->on_rq) { cfs_rq->runnable_load_avg += contrib_delta; cfs_rq->utilization_load_avg += utilization_delta; } I guess, these two things somehow belonged together to achieve this load/util propagation. >> And always propagating everyrthing up will indeed also fix the >> utilization issue. >> >> Of course, doing that propagation has its costs.. > > yes, that's the counterpart > >> >> Didn't you post a patch doing just this a while ago? > > My patch was doing that but only for utilization and i have start to > work on adding the propagation of load as well >