lec11_dp2 - Priority-Driven Scheduling of Periodic Tasks -...

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1 Priority-Driven Scheduling of Periodic Tasks - Chapter 6 – (Dynamic Priority (2)) Summary All of the above schedulability check works only under limited conditions – Preemptable at any time – Context switch overhead is negligible – Scheduling decision is made immediately upon jobs release and completion Practical Issues – What if the deadline is earlier than the period? – What if there is a non-preemptable code section (e.g., system call)? – What if the context switch overhead is not negligible? – Tick scheduling? – Precedence constraints
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2 EDF with deadlines less than periods • Quiz: can you find an easy but sufficient schedulability condition for a task set with deadlines less than periods? period decrease ; 1 time execution increase ; 1 1 1 + < = = n j j j n j j j j j i i D e p D p e p D Non-preemptable code section • a non-preemptable code section (NPS) of a low priority task blocks high priority task – How to take this into account in utilization bound check? tasks) all (for check single ; 1 max ) for task (only check by task task ; 1 / * if /* max deadline relative shorter with job a block can deadline relative longer with job Only : 1 1 1 1 + + < < = = = = + = j j n j n j j j i i n j j j k i j n i j i i i k k p b p e i p b p e k i D D NPS b D J D J Theorem
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3 Earlier deadline and Non- preemptable code section tasks) all (for check single ; 1 ) , min( max ) , min( ) for task (only check by task task ; 1 ) , min( ) , min( 1 1 1 + + = = = j i j n j n j j j j i i i n j j j j p D b p D e i p D b p D e Precedence constraints • Precedence relation says you can’t start until your
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This note was uploaded on 07/02/2008 for the course COMPUTER S 664 taught by Professor Leechangkyu during the Spring '08 term at Korea University.

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lec11_dp2 - Priority-Driven Scheduling of Periodic Tasks -...

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