PS_AVAILABLE_CPUS_CHANGE_CALLBACK function (wdm.h)

2025-08-06

The PS_AVAILABLE_CPUS_CHANGE_CALLBACK function is a callback routine that is called when the set of available CPUs changes for a process or the system.

Syntax

void PS_AVAILABLE_CPUS_CHANGE_CALLBACK(
                 PVOID Parameter
);

Parameters

Parameter

Return value

None

Remarks

This callback function is implemented by the driver and is called by the system when CPU availability changes.

The callback can be invoked at IRQL from PASSIVE_LEVEL to DISPATCH_LEVEL, so the implementation must be able to run at DISPATCH_LEVEL.

When the Callback is Invoked

The callback is invoked when:

CPUs are added or removed from the system (hotplug scenarios)
Process affinity is modified (for process-specific registrations)
System-wide CPU availability changes (for system registrations)
CPU cores go online or offline
Processor groups are modified

Implementation Guidelines

The callback should complete quickly since it may be called at DISPATCH_LEVEL
Avoid blocking operations or lengthy processing
Use the SequenceNumber parameter to detect and handle changes efficiently
Query the current CPU availability using PsQueryProcessAvailableCpus or PsQuerySystemAvailableCpus if needed

Requirements

Requirement	Value
Header	wdm.h
IRQL	PASSIVE_LEVEL to DISPATCH_LEVEL

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