10 Questions
What is the main characteristic of a batch process according to the text?
Runs silently without user input
In the context of scheduling, what is the impact of an interactive process on a batch process?
Batch process is preemptioned by the interactive process
What problem arises in the context of ready queues scheduling according to the text?
Starvation for lower priority processes
What does the term 'convoy effect' refer to in the context described?
Synchronization of processes that arrive together
Which statement best describes the role of priority in the scheduling algorithms discussed?
Priority determines which process gets to execute first
What does RR stand for in 'Priority RR MLQ MLFQ' as mentioned in the text?
Round-Robin
What feature distinguishes SJF (Shortest Job First) scheduling from other scheduling algorithms?
'SJF' always selects the shortest job next
How does a Light-weight process differ from a regular thread within a process?
'Light-weight process' is an independent path of execution within a process
'Complex Yes Yes' in 'Comparison: FCFS LEC-15' indicates what about the scheduling algorithm?
'Complex Yes Yes' allows preemptive scheduling and priority differentiation
What does 'MLQ MLFQ' signify in 'Priority RR MLQ MLFQ Complex No Yes PPriority Complex Yes Yes Simple No Yes Complex No Yes Complex Yes No Simple Yes No Complex Yes Yes Complex Yes Yes No No Yes No Yes Yes Yes Yes el PSJF C od eH Design Preemption Convoy effect Overhead SJF p'?
Multiple levels of queues implemented in the scheduler
Study Notes
Scheduling Algorithms
- A preemptive scheduling algorithm that is designed for time-sharing systems and doesn't depend on burst time (BT).
- The algorithm considers arrival time (AT) and time quantum (TQ) as criteria.
- No process will wait forever, providing low starvation and no convoy effect.
Multi-Level Queue (MLQ) Scheduling
- Ready queue is divided into multiple queues based on priority.
- A process is permanently assigned to one of the queues based on properties like memory size, process priority, or process type.
- Each queue has its own scheduling algorithm, for example, SP -> RR, IP -> RR, and BP -> FCFS.
Multi-Level Feedback Queue (MLFQ) Scheduling
- Multiple sub-queues are present, and a process can move between queues.
- The algorithm separates processes based on their burst time (BT) characteristics.
- If a process uses too much CPU time, it will be moved to a lower-priority queue.
- The scheme prevents I/O-bound and interactive processes from being moved to lower-priority queues.
- Less starvation occurs in MLFQ compared to MLQ, and it's flexible and configurable.
Page Replacement Algorithms
- Optimal page replacement finds the page that is never referenced in the future or one that is referenced farthest in the future.
- Least Recently Used (LRU) page replacement uses recent past as an approximation of the near future.
- LRU can be implemented using counters or a stack.
Concurrency
- Concurrency is the execution of multiple instruction sequences at the same time.
- It occurs in operating systems with multiple process threads running in parallel.
- A thread is a single sequence stream within a process and is used to achieve parallelism.
- Threads are light-weight processes used to divide a process's tasks into independent paths of execution.
Learn about Preemptive Multi-level Queue Scheduling (MLQ) also known as MLFQ. This scheduling algorithm is designed for time-sharing systems and is based on arrival time and time quantum. It aims to prevent processes from waiting indefinitely, resulting in low starvation and no convoy effect. With multiple priority-based queues in the ready queue, processes are assigned permanently based on priority.
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