Alan Jenkins wrote:
> Arjan van de Ven wrote:
>> Alan Jenkins wrote:
>>>> I notice that the "states:" is empty???
>>>>
>>> That confirms what powertop said. It's what I would expect.
>>
>> yeah the bios doesn't export C-states to the OS.
>>
>>> However, even with the fix, my BIOS doesn't provide any *C* state
>>> information. That's because the BIOS manages the different non-zero
>>> C-states itself, and linux doesn't see them.
>>>
>>> This is known as "C1E",
>>
>> that is only true for AMD systems btw; "C1E" is defined by AMD to be
>> "we'll break all the rules
>> and pick the C-state ourselves", on Intel systems C1E is "we'll go to
>> the lowest voltage in idle".
> I have an Core Duo 2 myself. I was mainly thinking of the difference
> between C1 on one core only, and C1 in both cores. The voltage has to be
> the same in both cores, and AFAIK it's the BIOS that ensures that, not
actually it's the hardware ;-)
> linux. E.g. for core 1, idle/C1 maps to two different states, with the
> lowest power state ("C1E") entered only if core 2 is also in C1.
to be nitpicking; this isn't called C1E.
On Intel systems, C1E *only* is the thing where you go to the lowest voltage
(and frequency) during idle.
What you're describing is often called "package C states", and yes they're
invisible to the OS.
(Afaik they only start to kick in for C3 and deeper, since lower C states don't
have package-wide effects;
only C3 and deeper for example impact the cache)
> I'd heard of AMD C1E problems but not read the explanation. Isn't C1E
> is invoked automatically on HLT? Some BIOS's don't even give you an
> option to disable it. I'd have thought going into C3 on HLT would have
> broken Windows (the versions that do use HLT).
Linux depends on things like the local apic timer more than those older windows
versions.
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