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
Lock variable with Priority Inversion problem
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*CS = Critical Section
In the case of a lock variable apart from the mutual exclusion problem, has another problem is called the priority inversion problem.
Due to the priority inversion problem spin lock occurs and the system is blocked due to spin lock.
Example:
We are considering the above lock variable code and two processes like P0 and P1.
Initially Lock =0 (CS is free).
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# P1 starts first and runs instructions 1,2 and 3 i.e. P1 is in the critical section and then preempted.
# Now P2 gets the CPU because P1 was preempted, then P2 tries to enter its critical section but stack on instruction 1 because still Lock = 1, P2 will be stacked on this loop until Lock = 0.
# Now CPU is busy with P2 to check the while loop continuously until Lock = 0.
#And Lock = 0 is only possible when P1 will get CPU to execute instruction 4, but CPU is busy with P2
P1 assign lock = 0 and leave the CS only when, P1 will get the CPU, and P2 will leave the CPU only when P2 enters into CS (when lock = 0) i.e. when P1 leaves the CS.
So, both processes are stopped; this concept is called spin lock.
It looks like a deadlock but it has a little bit of difference between deadlock and spin lock.
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Conclusion:
The lock mechanism is not suitable for the priority algorithm. But in the case of the Round Robin algorithm, it has no problem.
