linux-kernel - Re: [POC][RFC][PATCH] sched: Extended Scheduler Time Slice

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Message-ID: <82b0104f-1f05-44b0-9e95-57beecd541c8@kernel.org>
Date:   Thu, 26 Oct 2023 18:31:56 +0200
From:   Daniel Bristot de Oliveira <bristot@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Mateusz Guzik <mjguzik@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org,
        luto@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, willy@...radead.org, mgorman@...e.de,
        jon.grimm@....com, bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com,
        Joel Fernandes <joel@...lfernandes.org>,
        Youssef Esmat <youssefesmat@...omium.org>,
        Vineeth Pillai <vineethrp@...gle.com>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [POC][RFC][PATCH] sched: Extended Scheduler Time Slice

On 10/26/23 17:49, Steven Rostedt wrote:
> On Thu, 26 Oct 2023 09:40:35 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
>> Hence, why I don't want to associate this with priority inheritance. The
>> time constraint is a fundamental difference.
> 
> Let me add one more fundamental difference here that makes this solution
> different than priority inheritance and ceiling.
> 
> PI and ceiling define the correctness of the system. If you get it wrong or
> remove it, the system can be incorrect and lock up, fail deadlines, etc.
> There's hundreds, if not thousands of papers mathematically defining the
> correctness of PI, ceiling and proxy execution, as they are complex and
> critical for the system to behave properly.
> 
> This feature is a performance boost only, and has nothing to do with
> "correctness". That's because it has that arbitrary time where it can run a
> little more. It's more like the difference between having something in
> cache and a cache miss. This would cause many academics to quit and find a
> job in sales if they had to prove the correctness of an algorithm that gave
> you a boost for some random amount of time. The idea here is to help with
> performance. If it exists, great, your application will likely perform
> better. If it doesn't, no big deal, you may just have to deal with longer
> wait times on critical sections.

terminologies, terminologies.... those academic people :-)

I think that this can also be seen as an extension of the non-preemptive
mode to the user space, but... not entirely, it is a ceiling to the
[ higher than fair/lower than RT ] prior?

and it is not global. It is partitioned: once the section starts, it stays
there, being preempted by RT/DL?

[ trying to understand the implications of it ]

> 
> This is why I do not want to associate this as another form of PI or
> ceiling.
> 
> -- Steve