https://bugzilla.kernel.org/show_bug.cgi?id=17291


Len Brown <[email protected]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEEDINFO                    |REJECTED
          Component|Power-Processor             |BIOS
         Resolution|                            |DOCUMENTED
         AssignedTo|acpi_power-proces...@kernel |[email protected].
                   |-bugs.osdl.org              |org
            Summary|acpi_idle sees only c1 -    |acpi_idle sees only c1 -
                   |i7-875K                     |gigabyte GA-P55A-UD6
                   |                            |(Core-i7-875)




--- Comment #23 from Len Brown <[email protected]>  2010-11-30 05:44:09 ---
Thanks for verifying that acpi_idle can get into deep C-states
once they are enabled in the BIOS.

I can't explain why the BIOS for this board does not enable them
when you select the global SETUP defaults.  Perhaps a subsequent
version of the BIOS gets this right.

> ...if there is actually any point enabling
> EIST while using turbo mode and these extra C-states?

Yes.
see the output from turbostat -d -- it will tell you the LFM,
which is the low frequency mode associated with the lowest voltage
of the part.  That operating point is actually the most efficient
way to retire instructions.  The other operating points, including
all other P-states and all turbo states, are higher performance,
but also higher voltage, and thus -- by definition -- less efficient.
Without EIST, that high-efficiency operating point is not available.

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