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

[Ingo Molnar]

* Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx> wrote:

> On Wed, 18 Nov 2015 09:36:22 +0100
> Ingo Molnar <mingo@xxxxxxxxxx> 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
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