Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

Li, Aubrey
2017-07-17T13:41:16Z

On 2017/7/17 17:21, Peter Zijlstra wrote:
> On Fri, Jul 14, 2017 at 09:03:14AM -0700, Andi Kleen wrote:
>> fast idle doesn't have an upper bound.
>>
>> If the prediction exceeds the fast idle threshold any C state can be used.
>>
>> It's just another state (fast C1), but right now it has an own threshold
>> which may be different from standard C1.
>
> Given it uses the same estimate we end up with:
>
>
> Now, unless you're mister Turnbull, C2 will never get selected when
> fast_threshold > C2_threshold.
>
> Which is wrong. If you want to effectively scale the selection of C1,
> why not also change the C2 and further criteria.
>
That's not our intention, I think. As long as the predicted coming idle
period > threshold, we'll enter normal idle path, you can select any supported
c-states, tick can also be turned off for power saving. Any deferrable stuff
can be invoke as well because we'll sleep long enough.

Thanks,
-Aubrey