1. Lecture 8: CPU Scheduling
Joe McCarthy
CSS 430: Operating Systems - CPU Scheduling

2. Chapter 5: CPU Scheduling
Basic Concepts
Scheduling Criteria
Scheduling Algorithms
Thread Scheduling
Multiple-Processor Scheduling
Operating Systems Examples
Algorithm Evaluation
Material derived, in part, from Operating Systems Concepts with Java, 8th Ed. © 2009 Silberschatz, Galvin & Gagne
CSS 430: Operating Systems - CPU Scheduling

3. [from Chapter 1: Introduction]
CPU
[from Chapter 1: Introduction]
CSS 430: Operating Systems - CPU Scheduling

4. [from Chapter 1: Introduction]
CPU Scheduling
[from Chapter 1: Introduction]
CSS 430: Operating Systems - CPU Scheduling

5. [from Chapter 1: Introduction]
CPU Scheduling
[from Chapter 1: Introduction]
CSS 430: Operating Systems - CPU Scheduling

6. [from Chapter 1: Introduction]
CPU Scheduling
Multiprogramming
[from Chapter 1: Introduction]
CSS 430: Operating Systems - CPU Scheduling

7. [from Chapter 3: Processes]
CPU Scheduling
[from Chapter 3: Processes]
CSS 430: Operating Systems - CPU Scheduling

8. [from Chapter 3: Processes]
CPU Scheduling
Process Control Blocks
[from Chapter 3: Processes]
CSS 430: Operating Systems - CPU Scheduling

9. [from Chapter 3: Processes]
CPU Scheduling
Can all PCBs have access to CPU simultaneously?
[from Chapter 3: Processes]
CSS 430: Operating Systems - CPU Scheduling

10. [from Chapter 3: Processes]
CPU Scheduling
[from Chapter 3: Processes]
CSS 430: Operating Systems - CPU Scheduling

11. [from Chapter 3: Processes]
CPU Queues
[from Chapter 3: Processes]
CSS 430: Operating Systems - CPU Scheduling

12. [from Chapter 3: Processes]
Process States
[from Chapter 3: Processes]
CSS 430: Operating Systems - CPU Scheduling

13. CSS 430: Operating Systems - CPU Scheduling
Basic Concepts
Goal: Maximize CPU utilization via optimized multiprogramming
CPU–I/O Burst Cycle:
Process execution consists of a cycle of
CPU execution
I/O wait
CPU burst durations vary
Within a process, across different processes
CSS 430: Operating Systems - CPU Scheduling

14. Histogram of CPU-burst Durations
CSS 430: Operating Systems - CPU Scheduling

15. Alternating Sequence of CPU & I/O Bursts
CSS 430: Operating Systems - CPU Scheduling

16. CSS 430: Operating Systems - CPU Scheduling
CPU Scheduler
Selects next process to run (i.e., to get CPU time)
Dispatches that process (allocates the CPU to it)
CPU scheduler called when a process …
CSS 430: Operating Systems - CPU Scheduling

17. CSS 430: Operating Systems - CPU Scheduling
CPU Scheduler
Selects next process to run (i.e., to get CPU time)
Dispatches that process (allocates the CPU to it)
CPU scheduler called when a process:
Running  terminated
Running  waiting
Running  ready
Waiting  ready
Preemptive vs. non-preemptive
CSS 430: Operating Systems - CPU Scheduling

18. CSS 430: Operating Systems - CPU Scheduling
Dispatcher
Activates a process (gives control of the CPU to the process) selected by the short-term scheduler
Three steps:
CSS 430: Operating Systems - CPU Scheduling

19. CSS 430: Operating Systems - CPU Scheduling
Dispatcher
Activates a process (gives control of the CPU to the process) selected by the short-term scheduler
Three steps:
CSS 430: Operating Systems - CPU Scheduling

20. CSS 430: Operating Systems - CPU Scheduling
Dispatcher
Activates a process (gives control of the CPU to the process) selected by the short-term scheduler
Three steps:
Switch context
Switch to user mode
Jump to the proper location in user program to start/resume
CSS 430: Operating Systems - CPU Scheduling

21. CSS 430: Operating Systems - CPU Scheduling
Dispatcher
Activates a process (gives control of the CPU to the process) selected by the short-term scheduler
Three steps:
Switch context
Switch to user mode
Jump to the proper location in user program to start/resume
Dispatch latency?
CSS 430: Operating Systems - CPU Scheduling

22. CSS 430: Operating Systems - CPU Scheduling
Dispatcher
Activates a process (gives control of the CPU to the process) selected by the short-term scheduler
Three steps:
Switch context
Switch to user mode
Jump to the proper location in user program to start/resume
Dispatch latency: time it takes for the dispatcher to stop one user process and start another one
CSS 430: Operating Systems - CPU Scheduling

23. Scheduling Milestones
Submission Time
Time when job is submitted
E.g., when command is entered in shell
Admission Time
Time when job is admitted to Ready queue
PCB creation & other housekeeping has to take place
Activation Time
Time when job is first activated (Ready  Running)
E.g., when first output starts appearing on console
NB: may have several CPU-I/O burst cycles
Completion Time
Time when job finishes executing
CSS 430: Operating Systems - CPU Scheduling

24. Job (Process/Thread) Times
Response Time
Time before job is first activated
Activation Time – Submission Time
E.g., time between entering command & first response
Wait Time
Total amount of time job spends in Ready queue
Execution Time
Total amount of time job spends Running
NB: may have several CPU-I/O burst cycles
Turnaround Time
Time a job takes to complete after it is submitted
Completion Time – Submission Time
CSS 430: Operating Systems - CPU Scheduling

25. CSS 430: Operating Systems - CPU Scheduling
Scheduling Criteria
CPU utilization
% of time CPU is executing user processes
Throughput
# of processes that complete their execution per time unit
Average response time
average amount of between when a process is submitted & first response (for time-sharing environment)
Average waiting time
average amount of time a process waits in Ready queue
Average turnaround time
average amount of time to execute a process
CSS 430: Operating Systems - CPU Scheduling

26. Scheduling Optimization Criteria
CPU utilization: maximize
% of time CPU is executing user processes
Throughput: maximize
# of processes that complete their execution per time unit
Average response time: minimize
average amount of between when a process is submitted & first response (for time-sharing environment)
Average waiting time: minimize
average amount of time a process waits in Ready queue
Average turnaround time: minimize
average amount of time to execute a process
CSS 430: Operating Systems - CPU Scheduling

27. First-Come, First-Served (FCFS)
FCFS policy often implemented with FIFO queue
Example: 3 processes with the following burst times:
P1 = 24; P2 = 3; P3 = 3
Suppose that the processes arrive at t0 in the order: P1, P2, P3 The Gantt Chart for the schedule is:
Waiting times
Average waiting time: P1 P2 P3 24 27 30
CSS 430: Operating Systems - CPU Scheduling

28. First-Come, First-Served (FCFS)
FCFS policy often implemented with FIFO queue
Example: 3 processes with the following burst times:
P1 = 24; P2 = 3; P3 = 3
Suppose that the processes arrive at t0 in the order: P1, P2, P3 The Gantt Chart for the schedule is:
Waiting times: P1 = 0; P2 = 24; P3 = 27
Average waiting time: ( ) / 3 = 17.0 P1 P2 P3 24 27 30
CSS 430: Operating Systems - CPU Scheduling

29. CSS 430: Operating Systems - CPU Scheduling
FCFS Scheduling
Suppose that the processes arrive in the order:
P2 , P3 , P1
The Gantt chart for the schedule is:
Waiting times:
Average waiting time: P1 P3 P2 6 3 30
CSS 430: Operating Systems - CPU Scheduling

30. CSS 430: Operating Systems - CPU Scheduling
FCFS Scheduling
Suppose that the processes arrive in the order:
P2 , P3 , P1
The Gantt chart for the schedule is:
Waiting times: P1 = 6; P2 = 0;; P3 = 3
Average waiting time: ( ) / 3 = 3.0 P1 P3 P2 6 3 30
CSS 430: Operating Systems - CPU Scheduling

31. CSS 430: Operating Systems - CPU Scheduling
FCFS Scheduling P1 P2 P3 24 27 30 P1 P3 P2 6 3 30
Order: P1, P2, P3 Average wait: 17.0
Order: P2, P3, P1 Average wait: 3.0
Convoy effect: short process[es] stuck behind long process
How could we achieve minimal average waiting time?
CSS 430: Operating Systems - CPU Scheduling

32. Shortest-Job-First (SJF) Scheduling
Always schedule the shortest job first
Select process with shortest next CPU burst.
Optimal average waiting time
For any set of processes P1 P3 P2 6 3 30
CSS 430: Operating Systems - CPU Scheduling

33. CSS 430: Operating Systems - CPU Scheduling
Example of SJF
Process Arrival Time Burst Time P P P P
SJF scheduling chart
CSS 430: Operating Systems - CPU Scheduling

34. CSS 430: Operating Systems - CPU Scheduling
Example of SJF
Process Arrival Time Burst Time P P P P
SJF scheduling chart
Average waiting time: P4 P3 P1 3 16 9 P2 24
CSS 430: Operating Systems - CPU Scheduling

35. CSS 430: Operating Systems - CPU Scheduling
Example of SJF
Process Arrival Time Burst Time P P P P
SJF scheduling chart
Average waiting time: ( ) / 4 = 7.0 P4 P3 P1 3 16 9 P2 24
CSS 430: Operating Systems - CPU Scheduling

36. Shortest-Job-First (SJF) Scheduling
Always schedule the shortest job first
Select process with shortest next CPU burst.
Optimal average waiting time
For any set of processes
Only one problem P1 P3 P2 6 3 30
CSS 430: Operating Systems - CPU Scheduling

37. Shortest-Job-First (SJF) Scheduling
Always schedule the shortest job first
Select process with shortest next CPU burst.
Optimal average waiting time
For any set of processes
Only one problem P1 P3 P2 6 3 30
CSS 430: Operating Systems - CPU Scheduling

38. Shortest-Job-First (SJF) Scheduling
Always schedule the shortest job first
Select process with shortest next CPU burst.
Optimal average waiting time
For any set of processes
Only one problem
How to know the length of the next CPU burst? P1 P3 P2 6 3 30
CSS 430: Operating Systems - CPU Scheduling

39. Determining Length of Next CPU Burst
Can only estimate length of future bursts
Use exponential averaging of previous bursts
CSS 430: Operating Systems - CPU Scheduling

40. Predicting Length of Next CPU Burst
CSS 430: Operating Systems - CPU Scheduling

41. Examples of Exponential Averaging
 = 0
n+1 = n
Recent history does not count
 = 1
n+1 = tn
Only the most recent CPU burst counts
 = 0.5 (typically)
If we expand the formula, we get:
n+1 =  tn+(1 - ) tn -1 + …
+(1 -  )j  tn -j + …
+(1 -  )n +1 0
Since both  and (1 - ) are less than or equal to 1, each successive term has less weight than its predecessor
CSS 430: Operating Systems - CPU Scheduling

42. Shortest Remaining Time First
Pre-emptive version of SJF
CSS 430: Operating Systems - CPU Scheduling

43. Shortest Remaining Time First
Pre-emptive version of SJF
Average wait time?
CSS 430: Operating Systems - CPU Scheduling

44. Shortest Remaining Time First
Pre-emptive version of SJF
Average wait time: [(10 – 1) + (1 – 1) + (17 – 2) + (5 – 3)] / 4 = 6.5
CSS 430: Operating Systems - CPU Scheduling

45. Shortest Remaining Time First
Pre-emptive version of SJF
Average wait time: [(10 – 1) + (1 – 1) + (17 – 2) + (5 – 3)] / 4 = 6.5
Non pre-emptive SJF?
CSS 430: Operating Systems - CPU Scheduling

46. Shortest Remaining Time First
Pre-emptive version of SJF
Average wait time: [(10 – 1) + (1 – 1) + (17 – 2) + (5 – 3)] / 4 = 6.5
Non pre-emptive SJF: [0 + (8 – 1) + (17 – 2) + (12 – 3)] / 4 = 7.75
CSS 430: Operating Systems - CPU Scheduling

47. CSS 430: Operating Systems - CPU Scheduling
Priority Scheduling
A priority number (integer) is associated with each process
Based on internal and/or external factors
The CPU is allocated to the process with the highest priority
Preemptive: new, higher priority processes take precedence
Nonpreemptive: new processes wait for current process
Textbook: low #  high priority [opposite of ThreadOS]
SJF priority:
FCFS priority:
CSS 430: Operating Systems - CPU Scheduling

48. CSS 430: Operating Systems - CPU Scheduling
Priority Scheduling
A priority number (integer) is associated with each process
Based on internal and/or external factors
The CPU is allocated to the process with the highest priority
Preemptive: new, higher priority processes take precedence
Nonpreemptive: new processes wait for current process
Textbook: low #  high priority (opposite of ThreadOS)
SJF priority: predicted next CPU burst time
FCFS priority: arrival time
CSS 430: Operating Systems - CPU Scheduling

49. CSS 430: Operating Systems - CPU Scheduling
Priority Scheduling
A priority number (integer) is associated with each process
Based on internal and/or external factors
The CPU is allocated to the process with the highest priority
Preemptive: new, higher priority processes take precedence
Nonpreemptive: new processes wait for current process
Textbook: low #  high priority (opposite of ThreadOS)
SJF priority: predicted next CPU burst time
FCFS priority: arrival time
Problem?
CSS 430: Operating Systems - CPU Scheduling

50. CSS 430: Operating Systems - CPU Scheduling
Priority Scheduling
A priority number (integer) is associated with each process
Based on internal and/or external factors
The CPU is allocated to the process with the highest priority
Preemptive: new, higher priority processes take precedence
Nonpreemptive: new processes wait for current process
Textbook: low #  high priority (opposite of ThreadOS)
SJF priority: predicted next CPU burst time
FCFS priority: arrival time
Problem  Starvation – low priority processes may never execute
CSS 430: Operating Systems - CPU Scheduling

51. CSS 430: Operating Systems - CPU Scheduling
Priority Scheduling
A priority number (integer) is associated with each process
Based on internal and/or external factors
The CPU is allocated to the process with the highest priority
Preemptive: new, higher priority processes take precedence
Nonpreemptive: new processes wait for current process
Textbook: low #  high priority (opposite of ThreadOS)
SJF priority: predicted next CPU burst time
FCFS priority: arrival time
Problem  Starvation – low priority processes may never execute
Solution  Aging – as time progresses increase the priority of the process
CSS 430: Operating Systems - CPU Scheduling

52. Priority Scheduling Example
Average wait time: ( ) / 5 = 8.2
CSS 430: Operating Systems - CPU Scheduling

53. Priority Scheduling Example
Average wait time: ( ) / 5 = 8.2
If pre-emptive & process arrival times are 0, 1, 2, 3, 4?
Average wait time:
CSS 430: Operating Systems - CPU Scheduling

54. Priority Scheduling Example
Average wait time: ( ) / 5 = 8.2
If pre-emptive & process arrival times are 0, 1, 2, 3, 4?
Average wait time: [((2 – 1) + (9 – 4)) (16 – 2) + (18 – 3) + 0] / 5 = 7.0
CSS 430: Operating Systems - CPU Scheduling

55. CSS 430: Operating Systems - CPU Scheduling
Round Robin (RR)
Each process gets time quantum (q) of CPU time (typically ms)
Selected from head of Ready queue
If process does not block (I/O) within q ms: preempted
Added to the tail of the Ready queue (as are new processes)
General observations:
n processes in the Ready queue
each process gets 1/n of the CPU time (in slices of size q)
maximum waiting time: (n-1)q time units
CSS 430: Operating Systems - CPU Scheduling

56. Example of RR with Time Quantum = 4
Process Burst Time
P1 24
P2 3
P3 3
The Gantt chart is:
Compare to SJF: P1 P2 P3 4 7 10 14 18 22 26 30 P1 P3 P2 6 3 30
CSS 430: Operating Systems - CPU Scheduling

57. Time Quantum & Context Switch Time
Performance issues:
q large 
q small 
CSS 430: Operating Systems - CPU Scheduling

58. Time Quantum & Context Switch Time
Performance issues:
q large  FCFS
q small  context switch overhead too high
CSS 430: Operating Systems - CPU Scheduling

59. Time Quantum  Turnaround Time
CSS 430: Operating Systems - CPU Scheduling

60. CSS 430: Operating Systems - CPU Scheduling
Multilevel Queue
Ready queue can be partitioned into separate queues
E.g., foreground (interactive) & background (batch)
Each queue can have its own scheduling algorithm
Scheduling must be done between the queues
Simplest: Fixed priority scheduling
One possibility: 100% priority to foreground
Serve foreground if any; serve background only if no foreground
Problem?
CSS 430: Operating Systems - CPU Scheduling

61. CSS 430: Operating Systems - CPU Scheduling
Multilevel Queue
Ready queue can be partitioned into separate queues
E.g., foreground (interactive) & background (batch)
Each queue can have its own scheduling algorithm
Scheduling must be done between the queues
Simplest: Fixed priority scheduling
One possibility: 100% priority to foreground
Serve foreground if any; serve background only if no foreground
Problem: possibility of starvation
Another possibility?
CSS 430: Operating Systems - CPU Scheduling

62. CSS 430: Operating Systems - CPU Scheduling
Multilevel Queue
Ready queue can be partitioned into separate queues
E.g., foreground (interactive) & background (batch)
Each queue can have its own scheduling algorithm
Scheduling must be done between the queues
Simplest: Fixed priority scheduling
One possibility: 100% priority to foreground
Serve foreground if any; serve background only if no foreground
Problem: possibility of starvation.
Another possibility: 80/20 priority using time slices
80% to foreground using RR
20% to background using FCFS
CSS 430: Operating Systems - CPU Scheduling

63. Multilevel Queue Scheduling
CSS 430: Operating Systems - CPU Scheduling

64. Multilevel Feedback Queue
Process can migrate among queues
Queue placement based on past behavior (feedback)
Parameters:
number of queues
scheduling algorithms for each queue
when to upgrade a process
when to demote a process
when to select a queue for service
CSS 430: Operating Systems - CPU Scheduling

65. Multilevel Feedback Queue
CSS 430: Operating Systems - CPU Scheduling

66. Example of Multilevel Feedback Queue
Three queues: Q0, Q1, Q2; all use FCFS
If blocked for I/O, job returned to Q0 when I/O done
New jobs enter queue Q0
When activated (given CPU), job receives 8 milliseconds
If not done, job is preempted, demoted to queue Q1
Jobs in Q1
When activated, job receives 16 additional milliseconds
If not done, job is preempted, demoted to Q2
Jobs in Q2
When activated, job runs until terminated or interrupted
If not done, job is preempted, returned to Q2
CSS 430: Operating Systems - CPU Scheduling

67. Multiple-Processor Scheduling
CPU scheduling more complex when multiple CPUs are available
Homogeneous processors within a multiprocessor
Asymmetric multiprocessing: only one processor accesses the system data structures, alleviating the need for data sharing (master & slave processors)
Symmetric multiprocessing (SMP): each processor is self-scheduling, all processes in common ready queue, or each has its own private queue of ready processes
CSS 430: Operating Systems - CPU Scheduling

68. Multiple-Processor Scheduling
CPU scheduling more complex when multiple CPUs are available
Homogeneous processors within a multiprocessor
Asymmetric multiprocessing: only one processor accesses the system data structures, alleviating the need for data sharing (master & slave processors)
Symmetric multiprocessing (SMP): each processor is self-scheduling, all processes in common ready queue, or each has its own private queue of ready processes
Processor affinity?
CSS 430: Operating Systems - CPU Scheduling

69. Multiple-Processor Scheduling
CPU scheduling more complex when multiple CPUs are available
Homogeneous processors within a multiprocessor
Asymmetric multiprocessing: only one processor accesses the system data structures, alleviating the need for data sharing (master & slave processors)
Symmetric multiprocessing (SMP): each processor is self-scheduling, all processes in common ready queue, or each has its own private queue of ready processes
Processor affinity?
CSS 430: Operating Systems - CPU Scheduling

70. Multiple-Processor Scheduling
CPU scheduling more complex when multiple CPUs are available
Homogeneous processors within a multiprocessor
Asymmetric multiprocessing: only one processor accesses the system data structures, alleviating the need for data sharing (master & slave processors)
Symmetric multiprocessing (SMP): each processor is self-scheduling, all processes in common ready queue, or each has its own private queue of ready processes
Processor affinity: process has affinity for processor on which it is currently running
soft affinity: policy
hard affinity: mechanism
CSS 430: Operating Systems - CPU Scheduling

71. CSS 430: Operating Systems - CPU Scheduling
CSS 430: Operating Systems - CPU Scheduling

72. NUMA and CPU Scheduling
NUMA = non-uniform memory access
CSS 430: Operating Systems - CPU Scheduling

73. CSS 430: Operating Systems - CPU Scheduling
Multicore Processors
Multiple threads per core
Memory stall: CPU awaits instruction/data fetch
Multiple hardware threads: logical processors
Each logical processor can run a software thread
Enables progress to made on one thread while memory is updated
Two approaches
Coarse-grained multithreading (latency event)
Fine-grained multithreading (per instruction)
CSS 430: Operating Systems - CPU Scheduling

74. Multithreaded Multicore System
CSS 430: Operating Systems - CPU Scheduling

75. Operating System Examples
Solaris scheduling
Windows XP scheduling
Linux scheduling
CSS 430: Operating Systems - CPU Scheduling

76. CSS 430: Operating Systems - CPU Scheduling
Solaris Scheduling
Dispatch Table (for TS, IA)
CSS 430: Operating Systems - CPU Scheduling

77. CSS 430: Operating Systems - CPU Scheduling
Windows XP Scheduling
Priority classes
Relative priorities
Processes within a variable class (not real-time):
Expired time quantum  reduce priority
Released from wait  increase priority
Foreground process gets extra boost
CSS 430: Operating Systems - CPU Scheduling

78. Linux priorities & time quanta
CSS 430: Operating Systems - CPU Scheduling

79. runqueue: active & expired
When all task lists in active array are empty,
exchange active array & expired array
CSS 430: Operating Systems - CPU Scheduling

80. Java Thread Scheduling
Priority-based
FCFS within same priority level
May be preemptive or non-preemptive
A runnable thread executes until:
Time quantum expires
Blocks for I/O
Exits its run() method
Yields to another thread via yield()
“cooperative multitasking”
CSS 430: Operating Systems - CPU Scheduling

81. Java Thread Priorities
Values:
Thread.MAX_PRIORITY = 10
Thread.NORM_PRIORITY = 5
Thread.MIN_PRIORITY = 1
Methods:
int Thread.getPriority()
Thread.setPriority( int newPriority )
CSS 430: Operating Systems - CPU Scheduling

82. Mapping Java Thread Priorities
JVM runs on host
Java Thread priorities (user)  host kernel priorities
Example: Win32
CSS 430: Operating Systems - CPU Scheduling

83. CSS 430: Operating Systems - CPU Scheduling
Algorithm Evaluation
How can we compare scheduling algorithms?
CSS 430: Operating Systems - CPU Scheduling

84. CSS 430: Operating Systems - CPU Scheduling
Algorithm Evaluation
How can we compare scheduling algorithms?
FCFS, SJF & RR average wait times?
CSS 430: Operating Systems - CPU Scheduling

85. CSS 430: Operating Systems - CPU Scheduling
FCFS, SJF & RR: average wait times?
CSS 430: Operating Systems - CPU Scheduling

86. CSS 430: Operating Systems - CPU Scheduling
FCFS, SJF & RR: average wait times?
CSS 430: Operating Systems - CPU Scheduling

87. CSS 430: Operating Systems - CPU Scheduling
FCFS, SJF & RR: average wait times?
FCFS: ( ) / 5 = 28
CSS 430: Operating Systems - CPU Scheduling

88. CSS 430: Operating Systems - CPU Scheduling
FCFS, SJF & RR: average wait times?
FCFS: ( ) / 5 = 28
CSS 430: Operating Systems - CPU Scheduling

89. CSS 430: Operating Systems - CPU Scheduling
FCFS, SJF & RR: average wait times?
FCFS: ( ) / 5 = 28
SJF: ( ) / 5 = 13
CSS 430: Operating Systems - CPU Scheduling

90. CSS 430: Operating Systems - CPU Scheduling
FCFS, SJF & RR: average wait times?
FCFS: ( ) / 5 = 28
SJF: ( ) / 5 = 13
CSS 430: Operating Systems - CPU Scheduling

91. CSS 430: Operating Systems - CPU Scheduling
FCFS, SJF & RR: average wait times?
FCFS: ( ) / 5 = 28
SJF: ( ) / 5 = 13
RR: ( ) / 5 = 23
CSS 430: Operating Systems - CPU Scheduling

92. CSS 430: Operating Systems - CPU Scheduling
Algorithm Evaluation
How can we compare scheduling algorithms?
Analysis
Deterministic models: predetermined workload
CSS 430: Operating Systems - CPU Scheduling

93. CSS 430: Operating Systems - CPU Scheduling
Algorithm Evaluation
How can we compare scheduling algorithms?
Analysis
Deterministic models: predetermined workload
Queueing models: use probability distribution
Arrival rate
Service rate
CSS 430: Operating Systems - CPU Scheduling

94. CSS 430: Operating Systems - CPU Scheduling
Algorithm Evaluation
How can we compare scheduling algorithms?
Analysis
Deterministic models: predetermined workload
Queueing models: use probability distribution
Arrival rate
Service rate
Simulation
ThreadOS
CSS 430: Operating Systems - CPU Scheduling

95. CSS 430: Operating Systems - CPU Scheduling
Algorithm Evaluation
How can we compare scheduling algorithms?
Analysis
Deterministic models: predetermined workload
Queueing models: use probability distribution
Arrival rate
Service rate
Simulation
ThreadOS
Implementation
CSS 430: Operating Systems - CPU Scheduling

96. CSS 430: Operating Systems - CPU Scheduling
For next time
Readings
Chapter 4: Threads
Chapter 6: Process Synchronization
CSS 430: Operating Systems - CPU Scheduling