Re: [PATCH]new ACPI processor driver to force CPUs idle

[Len Brown <lenb@kernel.org>]

> Do you have some indicative data to show that arbitrary force-idling
> of hardware threads reduce power and heat?  It will be very good if
> this works without coordination among siblings.  Basically what you
> are saying is that running one or two of the force-idle threads in
> a 16-thread system provides significant reduction in power even
> without explicit methods to ensure that they idle sibling threads
> belonging to same core.

Re: siblings

Idling one HT sibling w/o idling the other saves almost very little power.
(On the flip side, the good news is that enabling HT consumes
 very little power:-)

So to save the most power possible,
the latest patch will attempt to idle 
threads in pairs of siblings.

But again, the driver is simply the messenger.  If the user
asks us to idle an odd number of threads, then one of them
will idle without idling its sibling.

cheers,
-Len Brown, Intel Open Source Technology Center