1. The Design , Implementation and Evaluation OF SMART : A Scheduler For Multimedia Applications
Jason Neih and Monica.S.Lam
Computer Science Laboratory, Stanford University
Sun Microsystems Laboratory
Presented by : Minal Dharod

2. AGENDA Introduction : Research Problem
Key Ideas, Design and Implementation
Evaluation : Experimental Results
Conclusion
Remarks

3. Why another Scheduling Algo??
Multimedia applications problems
Jitter, lip synchronization
Support:
Hardware: Special Instructions
Software support does not catch up….
RT schedulers :show unacceptable behavior
system lock up
User loses control

4. Needs of Real Time Tasks
Soft Real Time constraints
Meeting deadlines is important
Insatiable resource demand leading to Frequent overload
Movie playback at full resolution
Dynamically Adaptive Applications
Degrade QoS but meet deadlines
Co-existence
Fair allocation to RT and non- RT
User Preferences to be considered
Varying load
Varying importance
Teleconference Vs Television show

5. About SMART Problem of applications developers
Can specify service time, deadlines, degrading QoS, ask for timing information
Cannot tell system to meet deadline
What SMART does….provides USER INTERFACE
request notification for a deadline miss
Provides upcalls called notifications to user for responsive action
Gives user control over assigning priorities to tasks.

6. What is smart about SMART?
Takes two decisions :
Importance based on priority
Urgency based when a task needs to be executed
Value Tuple having Priority and Biased Virtual Finish Time (BVFT)
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7. Priority and BVFT Priority :
It’s a static quantity either supplied by the user or assigned a default value.
Biased Virtual Finishing Time :
Dynamic quantity the system uses to measure the degree to which each task has been allocated its proportional share of resources
Assigned a bias value
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Next

8. Terms and Their Meaning
Virtual Time :
Advances at a rate proportional to the amount of processing time it consumes divided by its share
Virtual Finishing Time :
Degree to which the task has been allocated its share of resources.
Queue Virtual Time:
Advances only if the task in queue is executing

9. Terms and Their Meaning
Earliest Deadline First Scheduling Algorithm :
A strategy for CPU or disk access scheduling. With EDF, the task with the earliest deadline is always executed first.
Best Effort Scheduling Algorithm :
Defines an order for the tasks in the working set in a way that if the tasks are executed in that order they would meet the deadlines.
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10. SMART’s Algorithm
If the task with highest value tuple is conventional task , schedule task
Else create candidate set of all real time tasks with higher value tuple than highest valued tuple conventional task
Apply best effort real time scheduling algorithm
Find task with earliest deadline whose execution does not cause any tasks with higher value tuples to miss deadlines.

11. SMART’s Algorithm
Consider eash candidate starting with one with highest tuple
Schedule the candidate into the working set which is initially empty.
Candidate is inserted in deadline order provided its execution does not cause any task to miss its deadline.
If a task cannot complete before the deadline send a notification to inform application that deadline cannot be met.

12. More on BVFT Task creation : Completing Quantum :
virtual time same as queue virtual time
BVFT is the queue virtual time + quantum assigned divided by the Share of the task.
Completing Quantum :
When a task finishes it is assigned a new quantum.
BVFT value is updated as :
last BVFT + quantum assigned divided by
the Share of the task.+ increased bias b divided by Share of task.

13. More on BVFT Conventional tasks have bias RT have zero bias BVFT
does not change allocation of resources
Affects instantaneous allocation of resources
Analogy to multi-level feedback scheduling algorithm

14. SMART – The Solution Provider!!!
Real Time Scheduling
Resource reservation and no admission control
SMART uses best effort scheduling
Optimal performance in underload
Can meet deadlines in overload
Fair Scheduling
Allocates resources in proportion to tasks
Performs poorly for RT : misses dealines in underload
Misses all deadlines in overload
SMART allows proportional sharing based on user desired allocations
Hierarchical Scheduling
All RT tasks have higer priority
Conventional Tasks have lower priority
SMART dynamically integrates both to ensure all important tasks get resources.

15. Experimental Results 2 sets of experiments :
Compare SMART to existing SVR4-RT and SVR4-TS , WFQ scheduling policies.
Test SMART capabilities :
Provide user predictable resource allocation controls
Adapt to dynamic workload changes
Deliver expected behavior for system not overloaded

16. Experimental Results(Contd)
Batch processing
Dhrystone benchmark
Quality measure is throughput
Interactive Processing
Typing- Emulation of user typing to text editor
Quality measure is response time
Real-Time Computations
Integrated Media Streams Player
News – Displays audio and video streams from local storage
Entertain – Processes video from local storage
Quality measure is no of deadlines met.

19. Highlights No need to write dynamic adaptive real time applications
Ability to co-operate with applications in managing resource to meet dynamic time constraints
Resource sharing
Gives freedom to users and take care of user preferences

20. Highlights ( Contd)
Differentiates between importance and urgency of real-time and conventional applications
Integrates priority for importance
Then urgency to optimize order for task service based on earliest-deadline first scheduling.

21. Remarks
The design is pretty simple but rich in its implementation result!!!!

22. Questions / Comments