* Matthew Garrett <mj...@srcf.ucam.org> wrote:
> On Tue, Aug 21, 2012 at 11:42:04AM +0200, Ingo Molnar wrote:
> > * Matthew Garrett <mj...@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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