[coreboot-gerrit] Change in coreboot[master]: mb/google/brya: Disable C state auto demotion for Brya & Brask

[Subrata Banik (Code Review)]

Attention is currently required from: Vinay Kumar, Maulik V Vaghela, Tim Wawrzynczak.
Subrata Banik has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/62630 )

Change subject: mb/google/brya: Disable C state auto demotion for Brya & Brask
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Patch Set 6:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/62630/comment/c965ea5f_fe7ca0e2 
PS5, Line 13: disabling this feature results in 110 mW power savings
> > Yes, no performance impact was seen with disabling autodemotion.
>
> Isn't that surprising? if I go by the current observation from your side about no perf impact and good power savings by disabling the C-state auto demotion/promotion, then what is the usefulness of this feature. Ideally this feature would provide better energy conservation when enable.

Is there any known limitation of C-state demotion/promotion is not impactful on ADL ? I had old data from few generation previous Intel platform that shows the perf/power analysis. There has to be some trade-off for sure but looking at above data, looks like this feature is not working as expected.