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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 54AF8C606AA for ; Mon, 8 Jul 2019 10:41:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2B5A720665 for ; Mon, 8 Jul 2019 10:41:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728358AbfGHKlT (ORCPT ); Mon, 8 Jul 2019 06:41:19 -0400 Received: from foss.arm.com ([217.140.110.172]:44302 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725836AbfGHKlT (ORCPT ); Mon, 8 Jul 2019 06:41:19 -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 9270E360; Mon, 8 Jul 2019 03:41:18 -0700 (PDT) Received: from [0.0.0.0] (e107985-lin.cambridge.arm.com [10.1.194.38]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EA2FE3F246; Mon, 8 Jul 2019 03:41:15 -0700 (PDT) Subject: Re: [RFC PATCH 2/6] sched/dl: Capacity-aware migrations To: luca abeni Cc: linux-kernel@vger.kernel.org, Greg Kroah-Hartman , "Rafael J . Wysocki" , Ingo Molnar , Peter Zijlstra , Vincent Guittot , "Paul E . McKenney" , Joel Fernandes , Quentin Perret , Luc Van Oostenryck , Morten Rasmussen , Juri Lelli , Daniel Bristot de Oliveira , Patrick Bellasi , Tommaso Cucinotta References: <20190506044836.2914-1-luca.abeni@santannapisa.it> <20190506044836.2914-3-luca.abeni@santannapisa.it> <20190708094136.7bce5f46@sweethome> From: Dietmar Eggemann Message-ID: <7d323b6f-ae15-b04d-cd67-a5e6f8d101d5@arm.com> Date: Mon, 8 Jul 2019 12:41:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190708094136.7bce5f46@sweethome> 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 7/8/19 9:41 AM, luca abeni wrote: > Hi Dietmar, > > On Thu, 4 Jul 2019 14:05:22 +0200 > Dietmar Eggemann wrote: > >> On 5/6/19 6:48 AM, Luca Abeni wrote: >> >> [...] >> >>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c >>> index 5b981eeeb944..3436f3d8fa8f 100644 >>> --- a/kernel/sched/deadline.c >>> +++ b/kernel/sched/deadline.c >>> @@ -1584,6 +1584,9 @@ select_task_rq_dl(struct task_struct *p, int >>> cpu, int sd_flag, int flags) if (sd_flag != SD_BALANCE_WAKE) >>> goto out; >>> >>> + if (dl_entity_is_special(&p->dl)) >>> + goto out; >> >> I wonder if this is really required. The if condition >> >> 1591 if (unlikely(dl_task(curr)) && >> 1592 (curr->nr_cpus_allowed < 2 || >> 1593 !dl_entity_preempt(&p->dl, &curr->dl)) && >> 1594 (p->nr_cpus_allowed > 1)) { >> >> further below uses '!dl_entity_preempt(&p->dl, &curr->dl))' which >> returns 'dl_entity_is_special(a) || ...' > > Uhm... I do not remember the details; I remember that the check fixed > something during the development of the patchset, but I did not check > if it was still needed when I forward-ported the patches... > > So, maybe it worked around some bugs in previous versions of the > kernel, but is not needed now. I figured it out in the meantime ... you added a ' ... || static_branch_unlikely(&sched_asym_cpucapacity)' in this patch to this if condition which let's special dl tasks (like sugov:X) enter this condition e.g. on big.LITTLE.