1. Flavius Gruian and Krzysztof Kuchcinski
Uncertainty Based Scheduling: Energy-Efficient Ordering for Tasks with Variable Execution Time
Flavius Gruian and Krzysztof Kuchcinski
Embedded Systems Design
Laboratory
Lund Institute of Technology
Sweden

2. ISLPED 2003 --- Uncertainty Based Scheduling…
Presentation Outline
Problem Set-up
A Motivation
Uncertainty Based Scheduling
Experiments
comparison to FullSearch
measurements on EVB80200 platform
Summary & Conclusions
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ISLPED Uncertainty Based Scheduling…

3. ISLPED 2003 --- Uncertainty Based Scheduling…
Problem Set-up
tasks: period=deadline, variable execution
off-line (static) ordering but
run-time speed selection
speed for the kth task
energy for a period (clock energy e(s)=Ks)
average energy
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4. A Motivational Example
Task Set: 3 tasks, uniform distribution (BCE,WCE) = {t1:(12,20),t2:(10,30),t3:(24,40)} A = 100, K=1, fref=1, b=2
Execution Type
<1, 3, 2>
42.094
41.839
134%
<2, 3, 1>
37.482
36.978
119%
Ideal: always mean
(speed 0.68)
100%
Offline WCE
(speed 0.90)
175%
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5. ISLPED 2003 --- Uncertainty Based Scheduling…
UBS in a Nutshell
Main ideas:
achieve a low speed ASAP by ordering tasks wisely
approximate by
Priority:
Observations:
prioritize short tasks
prioritize tasks with large variation in execution
prioritize power efficient tasks
algorithmic complexity O(N2) for ordering N tasks
Explain how we obtained the formula for the priority. Also why we approximate E like that.
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6. ISLPED 2003 --- Uncertainty Based Scheduling…
UBS vs. Full Search
300 sets of each size (3,4,5,6 tasks)
used the “real” E formula (4)
under 2% difference
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7. ISLPED 2003 --- Uncertainty Based Scheduling…
The Test Platform: EVB80200
Intel i80200 (XScale)
MAX1855 voltage regulator
32MB SDRAM, 4MB Flash
RS232, JTAG, 7segLED
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8. ISLPED 2003 --- Uncertainty Based Scheduling…
UBS example on i80200: m6
6 tasks
2 LZ (K=770mW)
2 QS (K=840mW)
2 FOR (K=800mW)
max speed time 49ms
variation 17ms
runtime rescheduling after every 5 x H
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9. More Experimental Results: m6
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10. Experimental Results: m15
5x LZ
5x QS
5x FOR
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11. ISLPED 2003 --- Uncertainty Based Scheduling…
Summary & Conclusions
use more information to derive better methods
UBS: runtime, non-intrusive ordering for tasks with variable execution time
measurements on
a real platform: EVB80200
realistic tasks: Lempel-Ziv codec & Quicksort
execution order matters!
random reordering: OK
UBS strategy: BEST
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12. ISLPED 2003 --- Uncertainty Based Scheduling…
Thank You!
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13. Measuring the core Power
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14. ISLPED 2003 --- Uncertainty Based Scheduling…
i80200 I/O Power
use the graph from Intel doc…
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15. ISLPED 2003 --- Uncertainty Based Scheduling…
i80200 Core Power
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16. ISLPED 2003 --- Uncertainty Based Scheduling…
UBO extension to EDF
Use preemption to extract regions
Push forward uncertain regions
Algorithm:
Start from the latest deadline
Between two consecutive deadlines order the regions according to the already given priorities
Preempt the task which does not fit entirely
Proceed with the next consecutive deadlines
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17. An Example of UBO EDF m=3 mean=9 Task 1 Task 2 WCE=10 WCE=6 T=16 D=15
Classic EDF 10 6
Preemption for Reduced Energy
Reordering
5 + 1
In the long run: 18% less energy than for the classic EDF!
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ISLPED Uncertainty Based Scheduling…