Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 886

than the performance_index returned by PAL_GET_PSTATE, the caller responds by
transitioning the processor to a lower performance P-state, which consumes less power
and operates at reduced performance.
Figure 13-6.
Current P-state =
Such an adaptive policy implemented by the caller to dynamically respond to system
workload characteristics using P-states allows for efficient power utilization – the
processor consumes additional power by operating at a higher performance level only
when the current workload requires it to do so.
2:638
Flowchart Showing P-state Feedback Policy
Reset Yes
busy ratio
newpstate Status == 0
(Accepted)
(1) getperfindex = PAL_GET_PSTATE
(2) OS computes newpstate index from
busy ratio and getperfindex
newpstate == getperfindex?
No
PAL_SET_PSTATE(newpstate)
Check
Return Code
Status == -2
Mark newpstate as Invalid
§
Status == 1
(Not Accepted)
(Invalid)
Volume 2, Part 2: Firmware Overview