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

From: Steve Muckle
Date: Wed Mar 16 2016 - 13:55:55 EST

On 03/16/2016 03:02 AM, Juri Lelli wrote:
> Hi,
> On 16/03/16 09:05, Peter Zijlstra 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 [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.
> I tend to agree here. To me the margin is something that we need to make
> this thing work and to get acceptable performance out of the box. So we
> can play with it while debugging, but I consider the schedtune slider as
> the way to tune the system at runtime.

Could the default schedtune value not serve as the out of the box margin?

Regardless I agree that a debug interface is the way to go for now while
we figure things out.