O(1) scheduler priority

140 priority level

Each process have scheduling class

A smaller value corresponds to a higher priority

based on

POSIX.4 root can only use SCHED_FIFO and SCHED_RR so conventional processes can use SCHED_OTHER

• [0,99]: priority for real-time tasks (SCHED_FIFO and SCHED_RR)

• [100,139]: priority for normal timesharing tasks (SCHED_OTHER or SCHED_NORMAL)

just have one ready queue so the complexity is

default user process priority is 120 (midpoint)

 

Static priority determines the length of a time slice

Dynamic priority

• To maintain good response time.

• favor I/O-bound process over CPU-bound process
• Processes which sleep a lot get a higher dynamic priority. (task’s interactivity)
• bonus reflects task’s interactivity or average sleep time