linux-kernel - Re: [PATCH 3/4] sched: introduce synchronized idle injection

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Date:	Tue, 24 Nov 2015 03:10:59 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Javi Merino <javi.merino@....com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Len Brown <len.brown@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Paul Turner <pjt@...gle.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Juri Lelli <Juri.Lelli@....com>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection

On Tue, 24 Nov 2015 11:09:56 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Nov 24, 2015 at 09:12:40AM +0000, Javi Merino wrote:
> > On Mon, Nov 23, 2015 at 07:07:06PM +0100, Peter Zijlstra wrote:
> > > On Mon, Nov 23, 2015 at 05:56:44PM +0000, Javi Merino wrote:
> > > > I've tested this series on Juno (2xCortex-A57 4xCortex-A53).
> > > > If you idle inject for 50% of the time, when I run 6 busy loops
> > > > the scheduler sometimes keeps two of them in the same cpu while
> > > > the another cpu is completely idle.  Without idle injection the
> > > > scheduler does the sensible thing: put one busy loop in each
> > > > CPU.  I'm running systemd and this only happens with
> > > > CONFIG_SCHED_AUTOGROUP=y.  If I unset CONFIG_SCHED_AUTOGROUP,
> > > > the tasks are spread across all cpus as usual.
> > > 
> > > That's not a plus for this patch though; but a bug report against
> > > AUTOGROUP/cgroup muck, right?
> > 
> > The bug only happens when you apply this series and you set the
> > system to idle inject 50% of the time.  SCHED_AUTOGROUP is already
> > part of the kernel and behaves properly with the kernel as is.  I
> > think that this patch should not introduce new bugs.
> 
> Ah, then I misunderstood your email, agreed.
First of all, thanks for testing.
Just trying to reproduce this. So let me understand your set up.
- 8 cores in total?
- you first set 50% idle
- then launch 6 busy loops
How often you see this happen?

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