Re: [PATCH] intel_idle: disable NHM/WSM HW C-state auto-demotion (v3)

From: Len Brown
Date: Mon Feb 28 2011 - 11:09:19 EST

> > Hardware C-state auto-demotion is a mechanism where the HW overrides
> > the OS C-state request, instead demoting to a shallower state,
> > which is less expensive, but saves less power.

> I'm interrested, for pytimechart, to have trace information of what
> actual c-state got reached after each idle request.
> Do you have any info on how to get that?

the actual c-state residency can be seen in the residency
counters that are exported by turbostat.
However, at the time of the request/return the OS doesn't know
that it's request got demoted demoted (or un-demoted).

No, checking the counters is not something we want to
add to the idle entry/exit path -- they are not optimized for speed.

Len Brown, Intel Open Source Technology Center

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