linux-kernel - Re: [PATCH 03/15] sched/fair: Add lag based placement

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Date:   Sat, 14 Oct 2023 10:08:00 +0200
From:   Mike Galbraith <efault@....de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Benjamin Segall <bsegall@...gle.com>
Cc:     mingo@...nel.org, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, 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, tglx@...utronix.de
Subject: Re: [PATCH 03/15] sched/fair: Add lag based placement

On Fri, 2023-10-13 at 18:35 +0200, Peter Zijlstra wrote:
> On Fri, Oct 13, 2023 at 12:34:28AM +0200, Peter Zijlstra wrote:
>
> > Right, so I do have this:
> >
> >   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=sched/eevdf&id=344944e06f11da25b49328825ed15fedd63036d3
> >
> > That allows tasks to sleep away the lag -- with all the gnarly bits that
> > sleep time has. And it reliably fixes the above. However, it also
> > depresses a bunch of other stuff. Never a free lunch etc.
> >
> > It is so far the least horrible of the things I've tried.
>
> So the below is one I conceptually like more -- except I hate the code,
> nor does it work as well as the one linked above.
>
> (Mike, this isn't the same one you saw before -- it's been 'improved')

Still improves high frequency switchers vs hogs nicely.

tbench vs massive_intr

6.4.16-stable                  avg
2353.57  2311.77  2399.27  2354.87  1.00

6.4.16-eevdf                   avg
2037.93  2014.57  2026.84  2026.44  .86   1.00  DELAY_DEQUEUE    v1
1893.53  1903.45  1851.57  1882.85  .79    .92  NO_DELAY_DEQUEUE
2193.33  2165.35  2201.82  2186.83  .92   1.07  DELAY_DEQUEUE    v2

It's barely visible in mixed youtube vs compute in i7-4790 box,
squinting required, and completely invisible in dinky rpi4.

A clear win along with no harm to the mundane mix is a good start in my
book.  Here's hoping canned benchmark bots don't grumble.

	-Mike