CREATE OWN LIBRARY
- Introduction: OS
- Booting Process
- Command Interpreter
- Dual mode of operation
- System Calls
- Difference between system call and library call
- Interrupt and Trap
- Introduction
- Scheduling Criteria, Terms and Concepts
- Different Type Scheduling Algorithms
- Longest Job First
- Longest Remaining Time First
- Highest Response Ratio Next (HRRN)
- Priority Scheduling
- Least Completed Next (LCN) Scheduling
- Multi-Level Queue Scheduling
- Multilevel Feedback Queue Scheduling
- Guaranteed Scheduling
- Fair Share Scheduling
- Lottery Scheduling
- Multi-Processor Scheduling
- Deadline Scheduling
- Rate-Monotonic Scheduling
- POSIX Real-Time Scheduling
- Priority Inversion
- Proportional Share Scheduling
- Comparison table of Scheduling Algorithm
- Algorithm Evaluation for Scheduling
- Important concept of MM
- Memory Representation as Address
- Memory layout for a Process
- Logical and Physical Address Space
- Necessity of Memory Management
- Introduction
- Concept of Non-contiguous memory allocation
- Basic concept of Paging
- Address Translation
- Process of Paging Method
- Calculation of Offset for paging
- Calculation of Logical Address Bit and number of Pages
- Calculation of Physical Address Bit and number of Frames
- Calculation of Page Table Size
- Organization of MMU
- Why Page size power of 2
- Paging Address Calculation: example1
- Paging Numeric Problem: Example2
- Paging Address Calculation: Example3
- Paging Address Calculation: Question1
- Some Important Question 2
- Paging Address Translation: Question3
- UGC NET Paging Question
- GATE Paging Question
- Number of information at Page Entry
- Exams Question on Page Entry Information
- Exam Question: Page Entry Information
- Calculates Page Table Entry Size
- Calculates Page Size
- Calculation of Optimal Page Size
- Question on Optimal Page Size
- Hashed Page Table with Example
- Inverted Page Table with Gate Question
- Question on Inverted Page Table
- Multi-Level Paging
- Multi-level paging: Example1
- Multi-level paging: Example2
- Allocation of Frames
- Subject Mock
Shortest Job First (SJF) / Shortest Request Next (SRN) Scheduling
SJF process and examples:
This algorithm associate with each process the length of the process's next CPU burst. When the CPU is available, it is assigned to the process that has the smallest next CPU burst. Thus, a request remains pending until all shorter requests have been serviced. If the next CPU bursts of two processes are the same, FCFS scheduling is used to break the tie.
Criteria - Burst time
Mode - Non-preemptive
Data-structure - Min Heap is the efficient data structure of SJF.
Example:
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Gantt chart:
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TAT = CT - AT and WT = TAT - BT
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SJF also suffers from the convoy effect i.e. if the larger process comes earlier then average waiting time will be increased.
Example 1: (Convoy effect)
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Example 2: (No convoy effect)
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In this example waiting time is 0 for all processes.
# The SJF scheduling algorithm is probably optimal, it gives a minimum average waiting time for a given set of processes.
# Overall throughput of every scheduling algorithm is same but at any point time if we stop and calculate then SJF is the best (gives maximum throughput).
# Practical implementation of SJF is not possible because burst time(Service time)of processes are not known to the operating system a priori, hence for OS, it is practically not possible to assign the shortest process to CPU from a set of processes in the ready queue.
# SJF Scheduling is used frequently in long-term scheduling. For long-term scheduling in a batch system, we can use the process time limit that a user specifies when he submits the job.
