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

Ingo Molnar
2015-11-27T09:17:15Z

* Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:

> On Wed, 18 Nov 2015 09:36:22 +0100
> Ingo Molnar <mingo@kernel.org> wrote:
>
> > >
> > > This patch introduces a scheduler based idle injection method, it
> > > works by blocking CFS runqueue synchronously and periodically. The
> > > actions on all online CPUs are orchestrated by per CPU hrtimers.
> > >
> > > Two sysctl knobs are given to the userspace for selecting the
> > > percentage of idle time as well as the forced idle duration for each
> > > idle period injected.
> >
> > What's the purpose of these knobs? Just testing, or will some
> > user-space daemon set them dynamically?
> >
> yes, it is to be used by userspace daemon such as thermal daemon.
> Though there are interests from in kernel thermal governor but that is
> another story.

Yeah, so let me make this very clear: for a kernel scheduling feature to be
self-sufficient is not 'another story', but a must-have aspect for this feature
to become upstream acceptable.

We don't add scheduler features that rely on pushing 'policy' to user-space.
That's poor design with many disadvantages. This feature should offer a reasonable
and automatic in-kernel default behavior with numbers that prove that it works.

Keeping an essential part of the feature in user-space earns a NAK from me.

Thanks,

Ingo