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SubjectRe: [discussion]sched: a rough proposal to enable power saving in scheduler
On Tue, Aug 21, 2012 at 11:42:04AM +0200, Ingo Molnar wrote:
> * Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> > [...] Putting this kind of policy in the kernel is an awful
> > idea. [...]
>
> A modern kernel better know what state the system is in: on
> battery or on AC power.

That's a fundamentally uninteresting thing for the kernel to know about.
AC/battery is just not an important power management policy input when
compared to various other things.

> > [...] It should never be altering policy itself, [...]
>
> The kernel/scheduler simply offers sensible defaults where it
> can. User-space can augment/modify/override that in any which
> way it wishes to.
>
> This stuff has not been properly sorted out in the last 10+
> years since we have battery driven devices, so we might as well
> start with the kernel offering sane default behavior where it
> can ...

Userspace has been doing a perfectly reasonable job of determining
policy here.

> > [...] because it'll get it wrong and people will file bugs
> > complaining that it got it wrong and the biggest case where
> > you *need* to be able to handle switching between performance
> > and power optimisations (your rack management unit just told
> > you that you're going to have to drop power consumption by
> > 20W) is one where the kernel doesn't have all the information
> > it needs to do this. So why bother at all?
>
> The point is to have a working default mechanism.

Your suggestions aren't a working default mechanism.

--
Matthew Garrett | mjg59@srcf.ucam.org


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