FOR FREE MATERIALS
- 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
Least Completed Next (LCN) scheduling
The LCN policy schedules the process that has consumed the least amount of CPU time.
Actually nature of a process, whether CPU-bound or I/O bound, and its CPU time requirement do not impact its progress in the scheduling system.
In this scheduling, all processes will make approximately equal progress in terms of the CPU time consumed by them.
Thus this scheduling policy guarantees that the short process will finish ahead of long processes.
The scheduler analyzes this information and selects the process that has yet consumed the least amount of CPU time.
In case of a tie, it selects the process that has not been serviced for the longest period of time.
Criteria: CPU Time (Burst Time)
Mode: Preemptive
Let’s take an example for better understanding.
Example 1:
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Gantt Chart as per Least Completed Next (LCN)
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# Arrival time of P1 is 0 so, P1 can get a whereas chance to CPU first up to 2 units because at unit 2 P2 comes in the ready queue. Now, when we compare P1 and P2, P1 already consumed CPU 2 unit where as P2 not consume any unit of CPU, So preempted P1 and CPU assign to process P2.
# Same procedure carry on to whole scheduling method that is the process which yet not consume CPU or consume the least amount of CPU, will schedule first.
Number of Context Switches (CS): 13
Now we calculate Turn Around Time (TAT) and Waiting Time (WT) using the following formula:
TAT = CT - AT, WT = TAT – BT
And
Response Time (RT) = FR (First Response) - AR (Arrival Time)
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Note: The response time for LCN is 0 for all process.
Advantage:
i) Response time is the least compared to other schedules.
ii) Shorter process finished first.
iii) Prediction of Burst time is not required like SJF, SRTF, and HRRN.
Disadvantage:
i) This policy has the familiar drawback of starving long processes of CPU attention.
ii) Time wastage for context switching is expensive.
