Definition
Processor Time
Processor time is the amount of time for which a central processing unit was used for processing instructions of a computer program or operating system, as opposed to elapsed time, which includes for example, waiting for input/output (I/O) operations or entering low-power (idle) mode.
The total processor time for a process is often split into:
- User CPU Time: Time spent executing instructions in user space.
- System CPU Time: Time spent by the kernel executing system calls on behalf of the process.
Visual Representation
Significance
Processor time is a critical metric for:
- Scheduling: The OS scheduler uses CPU time usage to ensure fairness among processes (see Timeouts).
- Performance Profiling: Identifying bottlenecks where a program spends excessive time in the “Running” state.
- Billing: In cloud computing and multi-user systems, users are often charged based on the processor time consumed rather than wall-clock time.