Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable
From: Rafael J. Wysocki
Date: Wed Mar 16 2016 - 08:45:28 EST
On Wed, Mar 16, 2016 at 9:05 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 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  (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
Agreed, plus it is quite hard to get ABI right from the outset. Even
if we decide on a sysfs knob, it still is unclear what exactly should
be represented by it in what units etc.