Volume 2, Part 1: Processor Abstraction Layer
2:397
PAL_GET_PSTATE
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
Table 11-81. PAL_GET_PSTATE
type
Argument
type
Description
0
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.
1
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
Section 11.6.1, “Power/Performance States
for more details on how the weighted average value is derived.
2
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.
3
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
for more information about
variable P-state performance.
All Other Values Reserved
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