Re: [RFC PATCH 0/3] CFS idle injection

Peter Zijlstra
2015-11-09T14:15:44Z

On Mon, Nov 09, 2015 at 11:56:51AM +0000, Punit Agrawal wrote:
> Jacob Pan <jacob.jun.pan@linux.intel.com> writes:
> > My take is that RT and throttling will never go well together since they
> > are conflicting in principle.
>
> I am not sure I follow. If RT (or other higher priority classes) can't
> be throttled then the CPUs are not able to contribute towards
> constraining power consumption and hence temperature.
>
> This is especially true in certain platforms where tasks belong to the
> RT class to maintain user experience, e.g., audio and video.

Audio/Video playback generally doesn't take a _lot_ of time these days.
What is important though is _when_ it happens.

And media playback typically already has a very well defined and stable
cadence (24Hz or whatnot). What you want is for your idle injector to
sync up with that, not disrupt it.

For other workloads, missing a deadline is about as bad as destroying
the chip, complete system shutdown might be safer than getting delayed.
(The very tired scenario of a saw, a laser and your finger; you want to
shut down the entire machine rather than just cut off your finger.)