The on-demand scanner (ODS) uses Windows Priority Control. The ODS
System Utilization setting does not set a static percentage of CPU utilization or threshold for CPU used to perform an ODS. Instead, the operating system manages the amount of CPU resources that the ODS receives at any point in the scan process.
The
System Utilization option in the
Performance tab for the ODS maps to
Windows Priority Control. The logic that Windows Priority Control uses keeps the CPU as busy as possible performing useful tasks. Windows Priority Control prioritizes CPU utilization to complete specific tasks in the shortest time possible, based on priority. Tasks must be prioritized to determine how available system resources are allocated.
A core component of Windows Priority Control is the
System Scheduler. The System Scheduler uses a Multilevel Feedback Queue algorithm to check the
Priority and the length of time needed to complete a task. Windows Priority Control allocates system resources based on this algorithm. When an ODS is set to run at
Below Normal, it does not take CPU time from programs that run at
Normal priority. If set to
idle, it does not take CPU from any other task or process running at a higher priority.
Why does the ODS use up to 100% CPU when the task is set to a System Utilization of Low?
When an ODS occurs, Windows Priority Control allocates CPU time to the ODS. How Windows Priority Control allocates CPU is based on the Scheduling Priority for the running task. The task priority of the ODS can be set in the ODS task or policy under Performance > System Utilization.
The following Microsoft article explains how Windows Priority Control works:
https://msdn.microsoft.com/en-us/library/windows/desktop/ms685100(v=vs.85).aspx
NOTE: The priority does not apply to archive files if archive scanning is enabled.
To view the priority of a task:
- Press Ctrl+Alt+Del, then select Task Manager.
- In the Processes tab, right-click the process and highlight Set Priority.
