linux-kernel - Re: [PATCH 10/24] sched/uclamg: Handle delayed dequeue

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Message-ID: <20240911091328.GM4723@noisy.programming.kicks-ass.net>
Date: Wed, 11 Sep 2024 11:13:28 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mike Galbraith <efault@....de>
Cc: Luis Machado <luis.machado@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Hongyan Xia <hongyan.xia2@....com>, mingo@...hat.com,
	juri.lelli@...hat.com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org,
	kprateek.nayak@....com, wuyun.abel@...edance.com,
	youssefesmat@...omium.org, tglx@...utronix.de
Subject: Re: [PATCH 10/24] sched/uclamg: Handle delayed dequeue

On Wed, Sep 11, 2024 at 11:10:26AM +0200, Mike Galbraith wrote:
> On Wed, 2024-09-11 at 10:45 +0200, Peter Zijlstra wrote:
> > On Wed, Sep 11, 2024 at 09:35:16AM +0100, Luis Machado wrote:
> > > > 
> > > > I'm assuming that removing the usage sites restores function?
> > > 
> > > It does restore function if we remove the usage.
> > > 
> > > From an initial look:
> > > 
> > > cat /sys/kernel/debug/sched/debug | grep -i delay                                                                                                                                                                                                                             
> > >   .h_nr_delayed                  : -4
> > >   .h_nr_delayed                  : -6
> > >   .h_nr_delayed                  : -1
> > >   .h_nr_delayed                  : -6
> > >   .h_nr_delayed                  : -1
> > >   .h_nr_delayed                  : -1
> > >   .h_nr_delayed                  : -5
> > >   .h_nr_delayed                  : -6
> > > 
> > > So probably an unexpected decrement or lack of an increment somewhere.
> > 
> > Yeah, that's buggered. Ok, I'll go rebase sched/core and take this patch
> > out. I'll see if I can reproduce that.
> 
> Hm, would be interesting to know how the heck he's triggering that.
> 
> My x86_64 box refuses to produce any such artifacts with anything I've
> tossed at it, including full LTP with enterprise RT and !RT configs,
> both in master and my local SLE15-SP7 branch.  Hohum.

Yeah, my hackbench runs also didn't show that. Perhaps something funny
with cgroups. I didn't test cgroup bandwidth for exanple.