Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754138AbbLOSp5 (ORCPT ); Tue, 15 Dec 2015 13:45:57 -0500 Received: from mail-pf0-f178.google.com ([209.85.192.178]:33038 "EHLO mail-pf0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753880AbbLOSpz (ORCPT ); Tue, 15 Dec 2015 13:45:55 -0500 Subject: Re: PELT initial task load and wake_up_new_task() To: Yuyang Du References: <566B8009.2090006@linaro.org> <20151213191319.GA28098@intel.com> <566F61AA.4020904@linaro.org> <20151215022432.GG28098@intel.com> Cc: Peter Zijlstra , Ingo Molnar , Morten Rasmussen , Dietmar Eggemann , Patrick Bellasi , Juri Lelli , Vincent Guittot , "linux-kernel@vger.kernel.org" From: Steve Muckle X-Enigmail-Draft-Status: N1110 Message-ID: <56705FE1.5000600@linaro.org> Date: Tue, 15 Dec 2015 10:45:53 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20151215022432.GG28098@intel.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1567 Lines: 35 On 12/14/2015 06:24 PM, Yuyang Du wrote: >>> On Fri, Dec 11, 2015 at 06:01:45PM -0800, Steve Muckle wrote: >>>> In init_entity_runnable_average() the last_update_time is initialized to >>>> zero. The task is given max load and utilization as a pessimistic >>>> initial estimate. >>>> >>>> But if in wake_up_new_task() the task is placed on a CPU other than >>>> where it was created, __update_load_avg() will be called via >>>> set_task_cpu() -> migrate_task_rq_fair() -> remove_entity_load_avg(). >>>> >>>> Since last_update_time is zero the delta will be huge and the task's >>>> load will be entirely decayed away before it is enqueued at the >>>> destination CPU. >>> >>> Since the new task's last_update_time is equal to 0, it will not be decayed. >> >> Can you point me to the code for that logic? I don't see anything that >> prevents the decay when a newly woken task is placed on a different CPU >> via the call chain I mentioned above. My testing also shows the load >> being decayed to zero. >> > You may search the last_update_time, and see it would be treated differently > if it is 0. Hope this may be helpful. Are you referring to the test in enqueue_entity_load_avg()? If so that isn't called until after remove_entity_load_avg() in this scenario, which has no check on last_update_time. thanks, Steve -- 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/