Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 645

Table 11-81. PAL_GET_PSTATE type Argument
type
0
1
2
3
All Other Values Reserved
For SCDD logical processors, or HIDD logical processors that do not support platform
power-caps, note that the performance_index returned for type=0 and type=3 will have
identical values. This is because the most recent PAL_SET_PSTATE procedure call that
returned a status of 0 will always succeed in transitioning to the requested performance
state for these coordination domains (see PAL_SET_PSTATE procedure description for
additional details).
For SCDD logical processors, the PAL_GET_PSTATE procedure should always be called
with type argument value of 0 or 3. On such processors, calling PAL_GET_PSTATE with
type argument value of 1 or 2 is undefined.
For HIDD logical processors, the type argument values of 1 and 2 are supported, since
such processors can also support platform power-caps, which affect the
weighted-average performance index.
If there was a thermal-throttling or hardware-initiated event (other than a platform
power-cap) which affected the processor power/performance for the current time
period, and the accuracy of the performance_index value has been impacted by the
event, then the procedure will return with status=1. The performance_index returned in
this case will still have a value that falls within the range of possible performance_index
values for this processor implementation (i.e., 0 up to the highest variable p-state
performance_index value).
The procedure, when called with type=1 or type=2, returns a fixed performance_index
value of 100 until the procedure has been called with type=1 to reset computation of
the weighted-average performance_index. For subsequent invocations with type=1 or
Volume 2, Part 1: Processor Abstraction Layer
The performance_index returned will correspond to the target P-state requested by software.
• For SCDD (software-coordinated dependency domain) logical processors, this is the
P-state requested by the most recent PAL_SET_PSTATE procedure call made by any
logical processor in the domain.
• For HCDD (hardware-coordinated dependency domain) or HIDD (hardware-independent
dependency domain) logical processors, this is simply the P-state requested by the most
recent PAL_SET_PSTATE procedure call on this logical processor.
The value returned is not affected by platform power-caps.
The performance_index is a weighted-average value of the different P-states that the
processor was operating in for the time duration between the current PAL_GET_PSTATE
procedure call, and the previous invocation of PAL_GET_PSTATE with type=1. This allows
the caller to establish a new starting point for subsequent computation of the
weighted-average performance_index. See
(P-states)" on page 2:315 for more details on how the weighted average value is derived.
The performance_index is a weighted-average value of the different P-states that the
processor was operating in for the time duration between the current PAL_GET_PSTATE
procedure call, and the previous invocation of PAL_GET_PSTATE with type=1. This allows
the caller to sample the current value of the performance_index, without affecting the starting
point used for computing the weighted-average performance_index.
The performance_index returned will correspond to the current instantaneous P-state of the
dependency domain containing the logical processor, at the time of the procedure call. The
value returned is not affected by platform power-caps. When variable P-states performance
is supported, the performance_index may be higher than the P-state requested. Please see
Section 11.6.1.4, "Variable P-state Performance" on page 2:322
variable P-state performance.
Description
Section 11.6.1, "Power/Performance States
for more information about
PAL_GET_PSTATE
2:397