Date: Tue, 24 Nov 2015 03:10:59 -0800
From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Javi Merino <javi.merino@arm.com>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        John Stultz <john.stultz@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Len Brown <len.brown@intel.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Eduardo Valentin <edubezval@gmail.com>, Paul Turner <pjt@google.com>,
        Morten Rasmussen <Morten.Rasmussen@arm.com>,
        Juri Lelli <Juri.Lelli@arm.com>, jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection
Message-ID: <20151124031059.3198b690@yairi>
In-Reply-To: <20151124100956.GR17308@twins.programming.kicks-ass.net>
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On Tue, 24 Nov 2015 11:09:56 +0100
Peter Zijlstra <peterz@infradead.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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