8.5. Processor Aggregator Device¶
The following section describes the definition and operation of the optional Processor Aggregator device. The Processor Aggregator Device provides a control point that enables the platform to perform specific processor configuration and control that applies to all processors in the platform.
The Plug and Play ID of the Processor Aggregator Device is ACPI000C.
Object |
Description |
|---|---|
_PUR |
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.
8.5.2. OSPM _OST Evaluation¶
When processing of the _PUR object evaluation completes, OSPM evaluates the _OST object, if present under the Processor Aggregator device, to convey _PUR evaluation status to the platform. _OST arguments specific to _PUR evaluation are described below.
Arguments: (3)
Arg0 - Source Event (Integer) : 0x80
Arg1 - Status Code (Integer) : see below
Arg2 - Idled Procs (Buffer) : see below
Return Value:
None
Argument Information:
Arg1 - Status Code:
0 -success - OSPM idled the number of logical processors indicated by the value of Arg2
1: no action was performed
Arg2 - A 4-byte buffer that represents a DWORD that is the number of logical processors that are now idled)
The platform may request a number of logical processors to be idled that exceeds the available number of logical processors that can be idled from an OSPM context for the following reasons:
The requested number is larger than the number of logical processors currently defined.
Not all the defined logical processors were onlined by the OS (for example. for licensing reasons)
Logical processors critical to OS function (for example, the BSP) cannot be idled.