Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

From: Peter Zijlstra
Date: Wed Mar 16 2016 - 04:05:18 EST

On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote:
> > Then again, maybe this knob will be part of the mythical
> > power-vs-performance slider?
> Patrick Bellasi's schedtune series [0] (which I think is the referenced
> mythical slider) aims to provide a more sophisticated interface for
> tuning scheduler-driven frequency selection. In addition to a global
> boost value it includes a cgroup controller as well for per-task tuning.
> I would definitely expect the margin/boost value to be modified at
> runtime, for example if the battery is running low, or the user wants
> 100% performance for a while, or the userspace framework wants to
> temporarily tailor the performance level for a particular set of tasks, etc.

OK, so how about we start with it as a debug knob, and once we have
experience and feel like it is indeed a useful runtime knob, we upgrade
it to ABI.

The problem with starting out as ABI is that its hard to take away