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

[Peter Zijlstra <peterz@infradead.org>]

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.