Re: [discussion]sched: a rough proposal to enable power saving in scheduler

[Arjan van de Ven <arjan@linux.intel.com>]

On 8/15/2012 6:14 PM, Rik van Riel wrote:
> On 08/15/2012 10:43 AM, Arjan van de Ven wrote:
> 
>> The easy cop-out is provide the sysadmin a slider.
>> The slightly less easy one is to (and we're taking this approach
>> in the new P state code we're working on) say "in the default
>> setting, we're going to sacrifice up to 5% performance from peak
>> to give you the best power savings within that performance loss budget"
>> (with a slider that can give you 0%, 2 1/2%  5% and 10%)
> 
> On a related note, I am looking at the c-state menu governor.
> 
> We seem to have issues there, with Linux often going into a much
> deeper C state than warranted, which can lead to a fairly steep
> performance penalty for some workloads.
> 

predicting the future is hard.
if you pick a too deep C state, you get a certain fixed performance hit
if you pick a too shallow C state, you get a pretty large power hit (depending on how long you actually stay idle)

also would need to know hw details; at least on Intel a bunch of things are done
by the firmware and some platforms we're not doing the right things as Linux
(or BIOS)