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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 autolearn=no 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 C993FC433E0 for ; Fri, 7 Aug 2020 13:55:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ACEA9221E2 for ; Fri, 7 Aug 2020 13:55:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726058AbgHGNzT (ORCPT ); Fri, 7 Aug 2020 09:55:19 -0400 Received: from ms01.santannapisa.it ([193.205.80.98]:22642 "EHLO mail.santannapisa.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725893AbgHGNzT (ORCPT ); Fri, 7 Aug 2020 09:55:19 -0400 Received: from [94.37.192.58] (account l.abeni@santannapisa.it HELO nowhere) by santannapisa.it (CommuniGate Pro SMTP 6.1.11) with ESMTPSA id 150297235; Fri, 07 Aug 2020 15:55:16 +0200 Date: Fri, 7 Aug 2020 15:55:10 +0200 From: luca abeni To: Juri Lelli Cc: peterz@infradead.org, mingo@redhat.com, rostedt@goodmis.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, tommaso.cucinotta@santannapisa.it, alessio.balsini@gmail.com, bristot@redhat.com, dietmar.eggemann@arm.com, linux-rt-users@vger.kernel.org, mtosatti@redhat.com, williams@redhat.com, valentin.schneider@arm.com Subject: Re: [RFC PATCH v2 6/6] sched/fair: Implement starvation monitor Message-ID: <20200807155510.2b380f49@nowhere> In-Reply-To: <20200807134353.GR42956@localhost.localdomain> References: <20200807095051.385985-1-juri.lelli@redhat.com> <20200807095604.GO42956@localhost.localdomain> <20200807152832.591f462e@nowhere> <20200807134353.GR42956@localhost.localdomain> Organization: Scuola Superiore S.Anna X-Mailer: Claws Mail 3.17.5 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Fri, 7 Aug 2020 15:43:53 +0200 Juri Lelli wrote: > On 07/08/20 15:28, luca abeni wrote: > > Hi Juri, > > > > On Fri, 7 Aug 2020 11:56:04 +0200 > > Juri Lelli wrote: > > > > > Starting deadline server for lower priority classes right away > > > when first task is enqueued might break guarantees > > > > Which guarantees are you thinking about, here? Response times of > > fixed priority tasks? > > Response time, but also wakeup latency (which, for better or worse, is > another important metric). > > > If fixed priority tasks are also scheduled through deadline servers, > > then you can provide response-time guarantees to them even when > > lower-priority/non-real-time tasks are scheduled through deadline > > servers. > > Right, but I fear we won't be able to keep current behavior for > wakeups: RT with highest prio always gets scheduled right away? Uhm... I think this depends on how the servers' parameters are designed: assigning "wrong" (or "bad") parameters to the server used to schedule RT tasks, this property is broken. (however, notice that even with the current patchset the highest priority task might be scheduled with some delay --- if the SCHED_OTHER deadline server is active because SCHED_OTHER tasks are being starved). Luca