From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 044DBC433F5 for ; Tue, 28 Aug 2018 14:54:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B23A12087B for ; Tue, 28 Aug 2018 14:54:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B23A12087B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728083AbeH1SqB (ORCPT ); Tue, 28 Aug 2018 14:46:01 -0400 Received: from foss.arm.com ([217.140.101.70]:39664 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727176AbeH1SqB (ORCPT ); Tue, 28 Aug 2018 14:46:01 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 819EA18A; Tue, 28 Aug 2018 07:53:59 -0700 (PDT) Received: from [10.1.37.73] (deggeman-mac.cambridge.arm.com [10.1.37.73]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5C1063F557; Tue, 28 Aug 2018 07:53:57 -0700 (PDT) Subject: Re: [PATCH] sched/fair: vruntime should normalize when switching from fair To: Peter Zijlstra , Steve Muckle Cc: Miguel de Dios , Ingo Molnar , linux-kernel@vger.kernel.org, kernel-team@android.com, Todd Kjos , Paul Turner , Quentin Perret , Patrick Bellasi , Chris Redpath , Morten Rasmussen , John Dias References: <20180817182728.76129-1-smuckle@google.com> <20180824093227.GN24124@hirez.programming.kicks-ass.net> <20180824094742.GJ24142@hirez.programming.kicks-ass.net> <20180827111458.GB24124@hirez.programming.kicks-ass.net> From: Dietmar Eggemann Message-ID: <2ed346fa-dbe8-4928-928b-a34338b2d8c9@arm.com> Date: Tue, 28 Aug 2018 15:53:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180827111458.GB24124@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/27/2018 12:14 PM, Peter Zijlstra wrote: > On Fri, Aug 24, 2018 at 02:24:48PM -0700, Steve Muckle wrote: >> On 08/24/2018 02:47 AM, Peter Zijlstra wrote: >>>>> On 08/17/2018 11:27 AM, Steve Muckle wrote: >>> >>>>>> When rt_mutex_setprio changes a task's scheduling class to RT, >>>>>> we're seeing cases where the task's vruntime is not updated >>>>>> correctly upon return to the fair class. >>> >>>>>> Specifically, the following is being observed: >>>>>> - task is deactivated while still in the fair class >>>>>> - task is boosted to RT via rt_mutex_setprio, which changes >>>>>> the task to RT and calls check_class_changed. >>>>>> - check_class_changed leads to detach_task_cfs_rq, at which point >>>>>> the vruntime_normalized check sees that the task's state is TASK_WAKING, >>>>>> which results in skipping the subtraction of the rq's min_vruntime >>>>>> from the task's vruntime >>>>>> - later, when the prio is deboosted and the task is moved back >>>>>> to the fair class, the fair rq's min_vruntime is added to >>>>>> the task's vruntime, even though it wasn't subtracted earlier. >>> >>> I'm thinking that is an incomplete scenario; where do we get to >>> TASK_WAKING. >> >> Yes there's a missing bit of context here at the beginning that the task to >> be boosted had already been put into TASK_WAKING. > > See, I'm confused... > > The only time TASK_WAKING is visible, is if we've done a remote wakeup > and it's 'stuck' on the remote wake_list. And in that case we've done > migrate_task_rq_fair() on it. > > So by the time either rt_mutex_setprio() or __sched_setscheduler() get > to calling check_class_changed(), under both pi_lock and rq->lock, the > vruntime_normalized() thing should be right. > > So please detail the exact scenario. Because I'm not seeing it. Using Steve's test program (https://lkml.org/lkml/2018/8/24/686) I see the issue but only if the two tasks (rt_task, fair_task) run on 2 cpus which don't share LLC (e.g. CPU0 and CPU4 on hikey960). So the wakeup goes the TTWU_QUEUE && !share_cache (ttwu_queue_remote) path. ... rt_task-3579 [000] 35.391573: sched_waking: comm=fair_task pid=3580 prio=120 target_cpu=004 rt_task-3579 [000] 35.391580: bprint: try_to_wake_up: try_to_wake_up: task=fair_task pid=3580 task_cpu(p)=4 p->on_rq=0 rt_task-3579 [000] 35.391584: bprint: try_to_wake_up: ttwu_queue: task=fair_task pid=3580 rt_task-3579 [000] 35.391588: bprint: try_to_wake_up: ttwu_queue_remote: task=fair_task pid=3580 rt_task-3579 [000] 35.391591: bprint: try_to_wake_up: ttwu_queue_remote: cpu=4 smp_send_reschedule rt_task-3579 [000] 35.391627: sched_pi_setprio: comm=fair_task pid=3580 oldprio=120 newprio=19 rt_task-3579 [000] 35.391635: bprint: rt_mutex_setprio: task=fair_task pid=3580 prio=120->19 queued=0 running=0 state=0x200 vruntime=46922871 cpu=4 cfs_rq->min_vruntime=7807420844 rt_task-3579 [000] 35.391641: bprint: rt_mutex_setprio: p->prio set: task=fair_task pid=3580 prio=19 queued=0 running=0 state=0x200 vruntime=46922871 rt_task-3579 [000] 35.391646: bprint: rt_mutex_setprio: queued checked: task=fair_task pid=3580 prio=19 queued=0 running=0 state=0x200 vruntime=46922871 rt_task-3579 [000] 35.391652: bprint: rt_mutex_setprio: running checked: task=fair_task pid=3580 prio=19 queued=0 running=0 state=0x200 vruntime=46922871 rt_task-3579 [000] 35.391657: bprint: rt_mutex_setprio: fair_class=0xffff000008da2c80 rt_class=0xffff000008da2d70 prev_class=0xffff000008da2c80 p->sched_class=0xffff000008da2d70 oldprio=120 p->prio=19 rt_task-3579 [000] 35.391661: bprint: detach_task_cfs_rq: task=fair_task pid=3580 cpu=4 vruntime_normalized=1 rt_task-3579 [000] 35.391706: sched_switch: rt_task:3579 [19] D ==> swapper/0:0 [120] -0 [004] 35.391828: bprint: ttwu_do_activate: ttwu_do_activate: task=fair_task pid=3580 -0 [004] 35.391832: bprint: ttwu_do_activate: ttwu_activate: task=fair_task pid=3580 -0 [004] 35.391833: bprint: ttwu_do_wakeup: ttwu_do_wakeup: task=fair_task pid=3580 -0 [004] 35.391834: sched_wakeup: fair_task:3580 [19] success=1 CPU:004 It doesn't happen on hikey960 when I use two cpus of the same LLC or on my laptop (i7-4750HQ).