linux-kernel - Re: [PATCH v4 6/7] sched/deadline: Deferrable dl server

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Message-ID: <20230908161140.GM19320@noisy.programming.kicks-ass.net>
Date:   Fri, 8 Sep 2023 18:11:40 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>
Cc:     Daniel Bristot de Oliveira <bristot@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joel Fernandes <joel@...lfernandes.org>,
        Vineeth Pillai <vineeth@...byteword.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH v4 6/7] sched/deadline: Deferrable dl server

On Fri, Sep 08, 2023 at 05:28:46PM +0200, Daniel Bristot de Oliveira wrote:

> Let me see if I got it:
> 
> 	- Always start the server, but throttled with full runtime...
> 	- Unconditionally decrement fair_server.dl_runtime from update_curr_fair()
> 		(check if it is not decremented twice as it runs)
> 	- When the dl timer fire, replenish or throttle for the next period?
> 
> is that the base for it?

Yes. So if dl timer fires and it still has runtime replenish will not
move the deadline and it will become eligible to run. If it has 0
runtime, replenish does it's thing, ups runtime and moves the deadline
forward and then the zero-laxity condition will re-throttle, goto 1
etc..