Lecture5 - Chapter 5: CPU Scheduling Operating System...

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Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition, Chapter 5: CPU Scheduling
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5.2 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Chapter 5: CPU Scheduling Basic Concepts Scheduling Criteria Scheduling Algorithms Thread Scheduling Multiple-Processor Scheduling Operating Systems Examples Algorithm Evaluation
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5.3 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Objectives To introduce CPU scheduling, which is the basis for multiprogrammed operating systems To describe various CPU-scheduling algorithms To discuss evaluation criteria for selecting a CPU-scheduling algorithm for a particular system
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5.4 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition CPU Scheduling Many hardware devices have scheduling to decide in which order operations are executed on the particular hardware CPU scheduling refers to the execution order of processes or threads on the CPU
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5.5 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Scheduling Processes or Threads It does not matter Scheduling policies apply the same to processes or threads
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5.6 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition PCB information The process state. The program counter, PC. The values of the different registers. The CPU scheduling information for the process. Memory management information regarding the process. Possible accounting information for this process. I/O status information of the process.
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5.7 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Context Switch/ Dispatcher Always do processes context switch if OS does not implement threads Need context switch of the whole PCB Perform kernel threads context switch if multithreading OS Context switch between threads in the same process is faster than context switching between processes. Context switch between threads from different processes still requires a process context switch
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5.8 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Costs for Context Switch The context (PCB) of a process is much heavier than for thread More info to copy during context switch Memory management is complex because processes do not share their memory Thread do not worry about accounting Threads share files, no change when context switch between threads Context switch between threads from different processes pay the same overhead as processes context switch
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5.9 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Processes characterization Processes spend some time executing instructions (computing) then makes some I/O request (read or write data to a file or to get input from a user).
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Lecture5 - Chapter 5: CPU Scheduling Operating System...

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