shortest first scheduling

Concept

Shortest Job First(SJF)

• select task with smallest total CPU time
• need to know CPU time required in advance
• minimize average waiting time

Predicting CPU time

• guess the future CPU time by the previous CPU-bound phases

1. simple average
   • previous runs need to be

2. exponential average
   • full history is stored in one value

Shortest Remaining Time(SRT)

• variation of SJF to handle new jobs dynamically
• new jobs with shorter remaining time can preempt current job
• serve short job first even if it arrives late