Re: [PATCH v6 7/7][Resend] cpufreq: schedutil: New governor based on scheduler utilization data

From: Peter Zijlstra
Date: Thu Mar 31 2016 - 08:24:54 EST

On Mon, Mar 28, 2016 at 11:17:44AM -0700, Steve Muckle wrote:
> The scenario I'm contemplating is that while a CPU-intensive task is
> running a thermal interrupt goes off. The driver for this thermal
> interrupt responds by capping fmax. If this happens just after the tick,
> it seems possible that we could wait a full tick before changing the
> frequency. Given a 10ms tick it could be rather annoying for thermal
> management algorithms on some platforms (I'm familiar with a few).

So I'm blissfully unaware of all the thermal stuffs we have; but it
looks like its somehow bolten onto cpufreq without feedback.

The thing I worry about is thermal scaling the CPU back past where RT/DL
tasks can still complete in time. It should not be able to do that, or
rather, missing deadlines because thermal is about as useful as
rebooting the device.

I guess I'm saying is, the whole cpufreq/thermal 'interface' needs work