Advanced Configuration and Power Interface Specification

Device Configuration
This optional object is used to describe proximity domains within a machine. _PXM evaluates to an
integer that identifies the device as belonging to a specific proximity domain. OSPM assumes that
two devices in the same proximity domain are tightly coupled. OSPM could choose to optimize its
behavior based on this. For example, in a system with four processors and six memory devices, there
might be two separate proximity domains (0 and 1), each with two processors and three memory
devices. In this case, the OS may decide to run some software threads on the processors in proximity
domain 0 and others on the processors in proximity domain 1. Furthermore, for performance
reasons, it could choose to allocate memory for those threads from the memory devices inside the
proximity domain common to the processor and the memory device rather than from a memory
device outside of the processor’s proximity domain. _PXM can be used to identify any device
belonging to a proximity domain. Children of a device belong to the same proximity domain as their
parent unless they contain an overriding _PXM. Proximity domains do not imply any ejection
relationships.
An OS makes no assumptions about the proximity or nearness of different proximity domains. The
difference between two integers representing separate proximity domains does not imply distance
between the proximity domains (in other words, proximity domain 1 is not assumed to be closer to
proximity domain 0 than proximity domain 6).
If the Local APIC ID / Local SAPIC ID / Local x2APIC ID or the GICC ACPI Processor UID of a
dynamically added processor is not present in the System Resource Affinity Table (SRAT), a _PXM
object must exist for the processor’s device or one of its ancestors in the ACPI Namespace.
Arguments:
None
Return Value:
An Integer (DWORD) containing a proximity domain identifier.
6.2.15 _SLI (System Locality Information)
The System Locality Information Table (SLIT) table defined in Section 5.2.17, “System Locality
Distance Information Table (SLIT)” provides relative distance information between all System
Localities for use during OS initialization.
The value of each Entry[i,j] in the SLIT table, where i represents a row of a matrix and j represents a
column of a matrix, indicates the relative distances from System Locality / Proximity Domain i to
every other System Locality j in the system (including itself).
The i,j row and column values correlate to the value returned by the _PXM object in the ACPI
namespace. See Section 6.2.14, “_PXM (Proximity)” for more information.
Dynamic runtime reconfiguration of the system may cause the distance between System Localities
to change.
_SLI is an optional object that enables the platform to provide the OS with updated relative System
Locality distance information at runtime. _SLI provide OSPM with an update of the relative distance
from System Locality i to all other System Localities in the system.
Arguments:
None
Version 6.0 325