Messages in this thread | | | Date | Tue, 21 Aug 2012 11:42:04 +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 Mon, Aug 20, 2012 at 10:06:06AM +0200, Ingo Molnar wrote: > > > If the answer is 'yes' then there's clear cases where the kernel > > (should) automatically know the events where we switch from > > balancing for performance to balancing for power: > > No. We can't identify all of these cases and we can't identify > corner cases. [...]
There's no need to identify 'all' of these cases - but if the kernel knows then it can have intelligent default behavior.
> [...] 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.
> [...] 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 ...
> [...] 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.
Thanks,
Ingo
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