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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B806ACA0ECA for ; Tue, 12 Sep 2023 11:57:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234888AbjILL5J (ORCPT ); Tue, 12 Sep 2023 07:57:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53246 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234910AbjILL5E (ORCPT ); Tue, 12 Sep 2023 07:57:04 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id D9ED9170B; Tue, 12 Sep 2023 04:56:56 -0700 (PDT) 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 BC342C15; Tue, 12 Sep 2023 04:57:33 -0700 (PDT) Received: from [10.57.93.149] (unknown [10.57.93.149]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 957213F67D; Tue, 12 Sep 2023 04:56:54 -0700 (PDT) Message-ID: <83b8c8d7-d53f-bea7-4ca3-5730d5c80b30@arm.com> Date: Tue, 12 Sep 2023 12:57:32 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.0 Subject: Re: [RFC PATCH 0/7] sched: cpufreq: Remove magic margins Content-Language: en-US To: Daniel Bristot de Oliveira Cc: Qais Yousef , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, "Rafael J. Wysocki" , Ingo Molnar , Dietmar Eggemann , Vincent Guittot , Peter Zijlstra , Viresh Kumar , juri.lelli@redhat.com References: <20230827233203.1315953-1-qyousef@layalina.io> <20230906211850.zyvk6qtt6fvpxaf3@airbuntu> <6011d8bb-9a3b-1435-30b0-d75b39bf5efa@arm.com> <20230907115307.GD10955@noisy.programming.kicks-ass.net> <89067f71-9b83-e647-053e-07f7d55b6529@arm.com> <20230907132906.GG10955@noisy.programming.kicks-ass.net> <5616e50d-b827-4547-5b16-9131ace98419@arm.com> <20230907133840.GH10955@noisy.programming.kicks-ass.net> <8657cc7c-169b-3479-5919-72bd39335b15@arm.com> <7c1cedb5-6342-1bf9-d1a6-3a87f63801fc@redhat.com> From: Lukasz Luba In-Reply-To: <7c1cedb5-6342-1bf9-d1a6-3a87f63801fc@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Daniel, On 9/8/23 13:51, Daniel Bristot de Oliveira wrote: > On 9/7/23 15:45, Lukasz Luba wrote: >>>>> RT literatur mostly methinks. Replacing WCET with a statistical model of >>>>> sorts is not uncommon, the argument goes that not everybody will have >>>>> their worst case at the same time and lows and highs can commonly cancel >>>>> out and this way we can cram a little more on the system. >>>>> >>>>> Typically this is proposed in the context of soft-realtime systems. >>>> >>>> Thanks Peter, I will dive into some books... >>> >>> I would look at academic papers, not sure any of that ever made it to >>> books, Daniel would know I suppose. >> >> Good hint, thanks! > > The key-words that came to my mind are: > > - mk-firm, where you accept m tasks will make their deadline > every k execution - like, because you run too long. > - mixed criticality with pWCET (probabilistic execution time) or > average execution time + an sporadic tail execution time for > the low criticality part. > > mk-firm smells like 2005's.. mixed criticality as 2015's..present. > > You will probably find more papers than books. Read the papers > as a source for inspiration... not necessarily as a definitive > solution. They generally proposed too restrictive task models. > > -- Daniel > Thanks for describing this context! That would save my time and avoid maybe sinking in this unknown water. As you said I might tread that as inspiration, since I don't fight with life-critical system, but a phone which needs 'nice user experience' (hopefully there are no people who disagree) ;) Regards, Lukasz