adaptive partition scheduler
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ADAPTIVE PARTITION SCHEDULER Nisari Balakrishnan S7 CS Roll No. 09412036
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CONTENTSPartitions
Advantages of partition
Why adaptive?
How CPU time divided between partition?
Underload
Free time
Full load
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CONTENTSAdvantages of APS
Adaptive partition Vs Static partition
Partition inheritance
Scheduling policies
How these policies are used?Adaptive partition in multiprocessing systemCase of multiprocessing system
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What are partitions?
They are virtual wall around a set of applications.
Each partition is given a particular cpu time.50% 20% 30%
Partition 1 Partition 2 Partition 3
Partition scheduler
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ADVANTAGES
Memory protectionOverload protection
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ADAPTIVE PARTITION SCHEDULER
Optional thread scheduler that guarantee min cpu time to processes.
Introduced by QNX OS.
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WHY ADAPTIVE?
We can dynamically launch an application into a partition
Child thread and child process automatically run in same partition as their parent.
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Adaptive partition scheduler was designed to solve two problems in embedded system design
i. Proper working in fully loaded condition.
ii.Prevent untrusted application from monopolizing the system.
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HOW CPU TIME DIVIDED BETWEEN PARTITIONS
It guarantees minimum amount of cpu time to partitions (overload).
It’s a preemptive priority-based scheduler (underload).
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UNDERLOAD
Partition demand less cpu time
Scheduler chooses partition based on priority.
Cpu time Critical time
Partition name
id budget used budget used
system 0 70% 6.23% 200ms 0.00ms
Pa 1 20% 15.56% 0ms 0.00ms
Pb 2 10% 5.23% 0ms 0.00ms
TOTAL 100% 27.02%
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Budget available
Blocked Ready
Blocked
Running
(Highest priority
ready thread)
6
6
8
9
6
7
6
10
4
Budget available
Blocked Ready
Blocked
Running
(Highest priority
ready thread)
6
6
8
9
6
7
6
10
4
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FREE TIME
Occurs when one partition isn’t running.
Cpu time Critical time
Partition name
id budget used budget used
system 0 70% .11% 200ms 0.00ms
Pa 1 20% 20.02% 0ms 0.00ms
Pb 2 10% 79.83% 0ms 0.00ms
TOTAL 100% 99.95%
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FULL LOAD
Occurs when all partitions demands their full budget.
Divides time between them by ratio of their budget
Cpu time Critical time
Partition name
id budget used budget used
system 0 70% 69.80% 200ms 0.00ms
Pa 1 20% 19.99% 0ms 0.00ms
Pb 2 10% 9.81% 0ms 0.00ms
TOTAL 100% 99.61%
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6
6
8
9
6
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6
10
4
Budget availableBudget exhausted
Blocked
Ready
Running (highest priority ready thread)
Blocked
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ADVANTAGES OF APSProvide cpu time guarantees when system is
heavily loadedUse realtime,priority-based scheduling when
system is lightly loaded.Make use of free cpu time.
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Overlay APS onto existing system without code changes.
Dynamically add and configure partitions at runtime.
Guarantees CPU cycles for recovery operations.
Stop malicious code from stealing all cpu time.
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ADAPTIVE PARTITION Vs STATIC PARTITION
Unlike static partition adaptive partition
i. Isn’t locked to a fixed set of code, we can add and configure partition.
ii.Avoid wastage of cpu time.
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PARTITION INHERITANCERun server thread in partition of their client
threadADVANTAGES
i. Enhance performance
ii.Avoid redesign of server budget when more clients are added.
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HOW THESE POLICIES ARE USED?Scheduler may: Stop a thread running before the end of its
timeslice (round-robin case)
OR
before thread has run to completion (FIFO case)
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ADAPTIVE PARTITION IN MULTIPROCESSING SYSTEM
On an SMP machine , APS considers time to be 100%.
APS first keep every processor busy , only then it apply budget.
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EXAMPLE
Thread 1 Thread 2 Thread 3 Thread 4
P.1
70%
P.2
10%
P.3
10% 10%
P.4
P.3 APS run all 4 threads all timeScheduler reports partition’s consumed time as 25%,25%,25%,25%
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WHAT’S THE CASE OF MULTITHRAEADED SYSTEM?
Method called runmask select cpu on which thread is allowed to run.
Not enough thread are permitted to run on a processor.
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CONCLUSIONAPS can guarantee minimum usage of cpu time
by each process.Increases maximum utilization of cpu time.Increases performance.In embedded systems APS
• ensures proper working in fully loaded condition.
• prevent unimportant application from monopolizing the system.
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REFERENCE
Wikipedia www.seminarprojects.com www.qnxsoftwaresystems.com
