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[23.128.96.18]) by mx.google.com with ESMTP id t5si8228971edr.374.2020.05.12.05.41.04; Tue, 12 May 2020 05:41:28 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729700AbgELMjS (ORCPT + 99 others); Tue, 12 May 2020 08:39:18 -0400 Received: from foss.arm.com ([217.140.110.172]:54178 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726891AbgELMjS (ORCPT ); Tue, 12 May 2020 08:39:18 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8BB6F30E; Tue, 12 May 2020 05:39:17 -0700 (PDT) Received: from [192.168.0.7] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F05103F71E; Tue, 12 May 2020 05:39:14 -0700 (PDT) Subject: Re: [PATCH v2 3/6] sched/deadline: Add dl_bw_capacity() To: Juri Lelli Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Steven Rostedt , Luca Abeni , Daniel Bristot de Oliveira , Wei Wang , Quentin Perret , Alessio Balsini , Pavan Kondeti , Patrick Bellasi , Morten Rasmussen , Valentin Schneider , Qais Yousef , linux-kernel@vger.kernel.org References: <20200427083709.30262-1-dietmar.eggemann@arm.com> <20200427083709.30262-4-dietmar.eggemann@arm.com> <23bde551-0d91-4bfe-ce65-40af9fbfdef9@arm.com> <20200506123738.GJ17381@localhost.localdomain> <20200511080122.GI264022@localhost.localdomain> From: Dietmar Eggemann Message-ID: <204d67f1-a21c-9d71-9b76-6f1a11c89092@arm.com> Date: Tue, 12 May 2020 14:39:13 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200511080122.GI264022@localhost.localdomain> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/05/2020 10:01, Juri Lelli wrote: > On 06/05/20 17:09, Dietmar Eggemann wrote: >> On 06/05/2020 14:37, Juri Lelli wrote: >>> On 06/05/20 12:54, Dietmar Eggemann wrote: >>>> On 27/04/2020 10:37, Dietmar Eggemann wrote: [...] >>> to say that we actually want to check new tasks bw requirement against >>> the available bandwidth of the particular CPU they happen to be running >>> (and will continue to run) when setscheduler is called. >> >> By 'available bandwidth of the particular CPU' you refer to >> '\Sum_{cpu_rq(i)->rd->span} CPU capacity', right? > > No. I was referring to the single CPU capacity. The capacity of the CPU > where a task is running when setscheduler is called for it (and DL AC > performed). See below, maybe more clear why I wondered about this case.. OK, got it! I was just confused since I don't think that this patch introduced the issue. Before the patch 'int cpus = dl_bw_cpus(task_cpu(p))' was used which returns the number of cpus on the (default) rd (n). So for a single CPU (1024) we use n*1024. I wonder if a fix for that should be part of this patch-set? [...] >> ... >> [ 144.920102] __dl_bw_capacity CPU3 rd->span=3-5 return 1338 >> [ 144.925607] sched_dl_overflow: [bash 1999] task_cpu(p)=3 cap=1338 cpus_ptr=3-5 > > So, here you are checking new task bw against 1338 which is 3*L > capacity. However, since load balance is disabled at this point for 3-5, > once admitted the task will only be able to run on CPU 3. Now, if more > tasks on CPU 3 are admitted the same way (up to 1338) I believe they > will start to experience deadline misses because only 446 will be > actually available to them until load balance is enabled below and they > are then free to migrate to CPUs 4 and 5. > > Does it makes sense? Yes, it does. So my first idea was to only consider the CPU (i.e. its CPU capacity) in case we detect 'cpu_rq(cpu)->rd == def_root_domain'? In case I re-enable load-balancing on cpuset '/', we can't make a task in cpuset 'B' DL since we hit this in __sched_setscheduler(): 4931 /* 4932 * Don't allow tasks with an affinity mask smaller than 4933 * the entire root_domain to become SCHED_DEADLINE. ... 4935 */ 4936 if (!cpumask_subset(span, p->cpus_ptr) || ... root@juno:~# echo 1 > /sys/fs/cgroup/cpuset/cpuset.sched_load_balance root@juno:~# echo $$ > /sys/fs/cgroup/cpuset/B/tasks root@juno:~# chrt -d --sched-runtime 8000 --sched-period 16000 -p 0 $$ chrt: failed to set pid 2316's policy: Operation not permitted So this task has to leave 'B' first I assume. [...]