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

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Message-ID: <ZAn9mfs0qgPtBr0r@hirez.programming.kicks-ass.net>
Date:   Thu, 9 Mar 2023 16:39:05 +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 04:29:04PM +0100, Peter Zijlstra wrote:
> On Thu, Mar 09, 2023 at 01:44:13PM +0100, Peter Zijlstra wrote:
> > 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...
> 
> So if I add TICK_NSEC based sleeper bonus (/2 for gentle), then starve
> works -- this is the absolutely minimal amount required. It sucks a bit
> it's HZ dependent, but alas.
> 
> Also, the whole sleeper bonus gets us back into needing to track the old
> vruntime and the overflow crap for super long sleeps and all that fugly
> :/ I was so hoping we could delete that code.
> 
> Oh well.
> 
> (also, did you know that removing the debug cruft helps with running
> numbers? ;-)

Also, it helps to turn the sched_feat on... clearly i should be calling
it a day.