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[82.53.135.115]) by smtp.gmail.com with ESMTPSA id qp3-20020a170907206300b0098cf565d98asm1001693ejb.22.2023.09.08.05.51.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Sep 2023 05:51:52 -0700 (PDT) Message-ID: <7c1cedb5-6342-1bf9-d1a6-3a87f63801fc@redhat.com> Date: Fri, 8 Sep 2023 14:51:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [RFC PATCH 0/7] sched: cpufreq: Remove magic margins Content-Language: en-US, pt-BR, it-IT To: Lukasz Luba , Peter Zijlstra Cc: Qais Yousef , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, "Rafael J. Wysocki" , Ingo Molnar , Dietmar Eggemann , Vincent Guittot , 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> From: Daniel Bristot de Oliveira In-Reply-To: <8657cc7c-169b-3479-5919-72bd39335b15@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org 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