8 cstates but only 4 to use?

I looked through the excellent Howto/FAQ provided by Glenn Ariel (thank you, sir), and he answered a lot of my questions, but was unable to find the answer to one remaining niggling curiosity.

The 'power' procfile lists a max_cstate of C8, but only lists C1-C4 as usable states to enter...I notice it is also this way in the example file output provided in Mr. Ariel's howto, so this must not be uncommon or new.

But, if 8 states are avaialble, why are only 4 in use?

this is a fixed upper limit.

And I figure it can't be just that no one ever thought to #define 5-9, that would be silly.

Thanks in advance, sorry if this is in a FAQ elsewhere, google is getting a lot of folks' dmesg output when I try to find answers along these lines.

David W. Hankins		"If you don't do it right the first time,
Software Engineer			you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

Hi,

max_cstate is the maximum the kernel would make use of if they were provided by the hardware and by the BIOS. However,

it is quite common that only one, two, three or -- at most! -- four of these states are actually available on a system. The ACPI core allows for eight to be ready for future systems which might have more than these four available.

Dominik