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

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Date:	Tue, 24 Nov 2015 09:12:40 +0000
From:	Javi Merino <javi.merino@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jacob Pan <jacob.jun.pan@...ux.intel.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>
Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection

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.

Cheers,
Javi
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