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

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

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?