Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait ornmi

[Arjan van de Ven]

On 6/5/2012 7:17 AM, Alan Stern wrote:
> On Mon, 4 Jun 2012, Arjan van de Ven wrote:
> 
>>> I disagree.  Deactivating a cpu for power saving is halfway to hotplug
>>> anyway.  I'd rather unify the two cases, where we can specify how dead a
>>> CPU should be, than have individual archs and boards do random hacks.
>>
>> well on PC's there really is no difference at least;
>> idle equals "all power removed" already there.
> 
> This doesn't sound right at all.  Len Brown has often told us that on
> Intel chips, power can't be removed from a package until _all_ the
> cores in the package are idle.

but "cpu hotplug" does not change that.. in fact, cpu hotplug is
implemented as a C state...


and to be specific; power will get removed from the cores one at a time.
you just cannot remove the power from the memory controller until the
last one is off.

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