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

Javi Merino
2015-11-24T09:12:48Z

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