linux-kernel - Re: [RFC PATCH 0/7] sched: cpufreq: Remove magic margins

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Message-ID: <7c1cedb5-6342-1bf9-d1a6-3a87f63801fc@redhat.com>
Date:   Fri, 8 Sep 2023 14:51:51 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Lukasz Luba <lukasz.luba@....com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Qais Yousef <qyousef@...alina.io>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>, juri.lelli@...hat.com
Subject: Re: [RFC PATCH 0/7] sched: cpufreq: Remove magic margins

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