CIS 630 OPERATING SYSTEMS

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CIS 630 OPERATING SYSTEMS
CHAPTER 5 Morty Kwestel 2003
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Chapter 5

• Scheduling
• Priority Based
• Modes
• Functions

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Chapter 5

• Scheduling
• Algorithms
• Distributed
• Priority Inversion

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FIGURE 5-1
Shared scheduler
Autonomous scheduler
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Scheduler
int P Priority Scheduler() while(CPU
! NULL) find highest P(ready_que) and
Get(proc) find free CPU if (CPU !
NULL) allocate_cpu (CPU, proc)  
while(P(proc1) gt P(proc2)) find
highest P(ready_que) and Get(proc1) find
lowest P(running) and Get(proc2) if
(P(proc1 gt proc2) preempt(proc1, proc2)

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Scheduling
P priority r time //time in system since
its arrival. t total service time a attained
service time q time quantum (TQ) e External
Priority
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Scheduling Functions
FIFO P r SJF P -t SRT P -(t
a) RR   p 0 ML p e MLF p n -
?log2 (a/T 1)? 1 RM p -d EDF p -(d
(r d))
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FIGURE 5-3
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MLF
n Priority level T time constant TQ n
i P 4 tp-0 a lt 20 T 1 T P
3 tp-1 a lt 21 T 3 T P 2 tp-2 a lt
22 T 7 T P 1 tp-3 a lt 23 T 15
T   Translates to a lt (2i 1 1) T
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MLF
Solve for i a/T lt 2i 1 1 a/T 1 lt 2i
1 log2 (a/T 1) lt i 1 i ?log2 (a/T 1)? -
1 P n i P n ( ?log2 (a/T 1)? 1)
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FIGURE 5-10
Priority inversion
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FIGURE 5-11
Priority Inheritance