Definition
Processor Time
Processor time is the duration a CPU was used processing instructions, as opposed to elapsed time (which includes I/O waits or idle mode).
Total processor time for a process is split into:
- User CPU Time: Instructions executed in user space
- System CPU Time: kernel executing system calls on behalf of the process
Significance
Scheduling
OS scheduler uses CPU time to ensure fairness among processes (see Timeouts).
Performance Profiling
Identifies bottlenecks where programs spend excessive time in “Running” state.
Billing
Cloud and multi-user systems charge based on processor time consumed, not wall-clock time.