Messages in this thread | | | Date | Tue, 21 Aug 2012 17:19:10 +0200 | From | Ingo Molnar <> | Subject | Re: [discussion]sched: a rough proposal to enable power saving in scheduler |
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* Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> 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. [...]
I disagree.
> [...] AC/battery is just not an important power management > policy input when compared to various other things.
Such as?
The thing is, when I use Linux on a laptop then AC/battery is *the* main policy input.
> > > [...] 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.
Has it properly switched the scheduler's balancing between power-effient and performance-maximizing strategies when for example a laptop's AC got unplugged/replugged?
> > > [...] 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.
In what way?
Thanks,
Ingo
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