Re: [RFC PATCH v2 0/2] Saving power by cpu evacuation sched_max_capacity_pct=n

Vaidyanathan Srinivasan
2009-05-14T14:59:44Z

* Andi Kleen <andi@firstfloor.org> [2009-05-13 17:10:54]:

> > > Yes that's fine and common, but you actually need to save power for this,
> > > which throttling doesn't do.
> > >
> > > My understanding this work is a extension of the existing
> > > sched_mc_power_savings features that tries to be optionally more
> > > aggressive to keep complete package idle so that package level
> > > power saving kicks in.
> > >
> > > I'm just requesting that they don't call that throttling.
> >
> > Ah no, this work differs in that regard in that it actually 'generates'
> > idle time, instead of optimizing idle time.
>
> That is what i meant with "more aggressive to keep complete packages idle"
> above.

Hi Andi,

There is a difference in the framework as Peter has mentioned, we are
trying to create idle times by forcefully reducing work. From an
end-user point of view, this can be seen as a logical extension of
sched_mc_power_savings... v1 of the RFC extends the framework.

However Ingo suggested that the knob is not intuitive and hence I have
tried to switch to a percentage knob sched_max_capacity_pct.

I am interested in an easy, simple and intuitive framework to evacuate
cores which may imply forcefully reducing (throttling) work.

> > Therefore it takes actual cpu time away from real work, which is
> > throttling. Granted, one could call it limiting or similar, but
> > throttling is a correct name.
>
> That will be always ongoing confusion with the existing established
> term.
>
> If you really need to call it throttling use "scheduler throttling"
> or something like that, but a different word would be better.

I think 'scheduler throttling' is good so that we avoid the term 'CPU
throttling' or core throttling. I had named this cpu evacuation or
core evacuation just to avoid confusion with hardware throttling.

--Vaidy