Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
Table 8-253 Processor Aggregator Device Objects
Object
_PUR
Description
Requests a number of logical processors to be placed in an idle state
8.5.1 Logical Processor Idling
In order to reduce the platform’s power consumption, the platform may direct OSPM to remove a
logical processor from the operating system scheduler’s list of processors where non-processor
affinitized work is dispatched. This capability is known as Logical Processor Idling and provides a
means to reduce platform power consumption without undergoing processor ejection / insertion
processing overhead. Interrupts directed to a logical processor and processor affinitized workloads
will impede the effectiveness of logical processor idling in reducing power consumption as OSPM is
not expected to re-target this work when a logical processor is idled.
8.5.1.1 PUR (Processor Utilization Request)
The _PUR object is an optional object that may be declared under the Processor Aggregator Device
and provides a means for the platform to indicate to OSPM the number of logical processors to be
idled. OSPM evaluates the _PUR object as a result of the processing of a Notify event on the
Processor Aggregator device object of type 0x80.
Arguments:
None
Return Value:
A Package as described below.
Return Value Information
Package
{
RevisionID // Integer: Current value is 1
NumProcessors // Integer
}
The NumProcessors package element conveys the number of logical processors that the platform
wants OSPM to idle. This number is an absolute value. OSPM increments or decrements the number
of logical processors placed in the idle state to equal the NumProcessors value as possible. A
NumProcessors value of zero causes OSPM to place all logical processor in the active state as
possible.
OSPM uses internal logical processor to physical core and package topology knowledge to idle
logical processors successively in an order that maximizes power reduction benefit from idling
requests. For example, all SMT threads constituting logical processors on a single processing core
should be idled to allow the core to enter a low power state before idling SMT threads constituting
logical processors on another core.
494 April, 2015 Version 6.0