linux-kernel - Re: [PATCH 6/9] sched/fair: Removed unsued cfs_rq.h_nr

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Message-ID: <20241128101517.GA12500@noisy.programming.kicks-ass.net>
Date: Thu, 28 Nov 2024 11:15:17 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: mingo@...hat.com, juri.lelli@...hat.com, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, linux-kernel@...r.kernel.org,
	kprateek.nayak@....com, pauld@...hat.com, efault@....de,
	luis.machado@....com
Subject: Re: [PATCH 6/9] sched/fair: Removed unsued cfs_rq.h_nr_delayed

On Thu, Nov 28, 2024 at 11:03:48AM +0100, Peter Zijlstra wrote:
> On Thu, Nov 28, 2024 at 10:27:47AM +0100, Vincent Guittot wrote:
> > h_nr_delayed is not used anymore. We now have
> > - h_nr_running which tracks tasks ready to run
> > - h_nr_enqueued which tracks enqueued tasks either ready to run or delayed
> >   dequeue
> 
> Oh, now I see where you're going.
> 
> Let me read the lot again, because this sure as hell was a confusing
> swizzle.

So the first patch adds h_nr_delayed.

Then confusion

Then we end up with:

 h_nr_enqueued = h_nr_running + h_nr_delayed

Where h_nr_enqueued is part of rq->nr_running (and somewhere along the
way you rename and remove some idle numbers).

Can't we structure it like:

  - add h_nr_delayed
  - rename h_nr_running to h_nr_queued
  - add h_nr_runnable = h_nr_queued - h_nr_delayed
  - use h_hr_runnable
  - remove h_nr_delayed

  - clean up idle muck


And I'm assuming this ordering is because people want h_nr_delayed
backported. Because the even more sensible order would be something
like:

 - rename h_nr_running into h_nr_queued
 - add h_nr_runnable (being h_nr_queued - h_nr_delayed, without ever
   having had h_nr_delayed).
 - use h_nr_runnable
 
 - clean up idle muck