Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
8.4.7.1.1.3 Reference Performance
Optional
Register or DWORD
Register Location: PCC or Functional Fixed Hardware
Attribute:
Read
Size:
8-32 bits
If supported by the platform, Reference Performance is the rate at which the Reference
Performance Counter increments. If not implemented (or zero), the Reference Performance Counter
increments at a rate corresponding to the Nominal Performance level.
8.4.7.1.1.4 Lowest Nonlinear Performance
Register or DWORD
Register Location:
Attribute:
Size:
PCC or Functional Fixed Hardware
Read
8-32 bits
Lowest Nonlinear Performance is the lowest performance level at which nonlinear power savings
are achieved, for example, due to the combined effects of voltage and frequency scaling. Above this
threshold, lower performance levels should be generally more energy efficient than higher
performance levels. In traditional terms, this represents the P-state range of performance levels.
This register effectively conveys the most efficient performance level to OSPM.
8.4.7.1.1.5 Lowest Performance
Register or DWORD
Register Location:
Attribute:
Size:
PCC or Functional Fixed Hardware
Read
8-32 bits
Lowest Performance is the absolute lowest performance level of the platform. Selecting a
performance level lower than the lowest nonlinear performance level may actually cause an
efficiency penalty, but should reduce the instantaneous power consumption of the processor. In
traditional terms, this represents the T-state range of performance levels.
8.4.7.1.1.6 Guaranteed Performance Register
Optional
Register Location:
Attribute:
Size:
PCC or Functional Fixed Hardware
Read
8-32 bits
Guaranteed Performance Register conveys to OSPM a Guaranteed Performance level, which is
the current maximum sustained performance level of a processor, taking into account all known
external constraints (power budgeting, thermal constraints, AC vs DC power source, etc.). All
processors are expected to be able to sustain their guaranteed performance levels simultaneously.
The guaranteed performance level is required to fall in the range [Lowest Performance, Nominal
performance], inclusive.
If this register is not implemented, and Autonomous Selection is not enabled, OSPM assumes
guaranteed performance is always equal to nominal performance.
Notify events of type 0x83 to the processor device object will cause OSPM to re-evaluate the
Guaranteed Performance Register. Changes to guaranteed performance should not be more frequent
than once per second. If the platform is not able to guarantee a given performance level for a
482 April, 2015 Version 6.0