linux-kernel - Re: [PATCH 10/10] sched/fair: Implement an EEVDF like policy

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Message-ID: <ZAnUnSEJ92bKpim7@hirez.programming.kicks-ass.net>
Date:   Thu, 9 Mar 2023 13:44:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mike Galbraith <efault@....de>
Cc:     mingo@...nel.org, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, corbet@....net,
        qyousef@...alina.io, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, pjt@...gle.com, pavel@....cz,
        qperret@...gle.com, tim.c.chen@...ux.intel.com, joshdon@...gle.com,
        timj@....org, kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, joel@...lfernandes.org
Subject: Re: [PATCH 10/10] sched/fair: Implement an EEVDF like policy

On Thu, Mar 09, 2023 at 10:06:33AM +0100, Peter Zijlstra wrote:
> Hi Mike!
> 
> On Wed, Mar 08, 2023 at 02:36:01PM +0100, Mike Galbraith wrote:
> > On Wed, 2023-03-08 at 09:39 +0100, Mike Galbraith wrote:
> > >
> > > Curiosity got the best of me...
> > 
> > Remember this little bugger, allegedly distilled from a real
> > application control thread starvation issue?
> 
> Oooh, yeah, I should still have that somewhere. I'll try and remember
> what exactly was needed to make it behave properly.

That thing wants both wakeup preemption and sleeper bonus. Specifically,
it needs the signal to insta-preempt the 'pointless' kill loop.

What happens is that while positive lag, we get this, when negative lag
happens wakeup-preemption is not achieved and we get delayed by a full
tick.

This gets us very little actual runtime.

Let me see what do do about that...