Uncertainty Based Scheduling: Energy-Efficient Ordering for Tasks with Variable Execution Time
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Transcript of Uncertainty Based Scheduling: Energy-Efficient Ordering for Tasks with Variable Execution Time
Uncertainty Based Scheduling:Uncertainty Based Scheduling:Energy-Efficient OrderingEnergy-Efficient Ordering
forforTasks with Variable Execution Tasks with Variable Execution
TimeTime
Flavius Gruian and Krzysztof Kuchcinski
Embedded Systems DesignLaboratory
Lund Institute of TechnologySweden
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Presentation OutlinePresentation Outline
• Problem Set-up• A Motivation• Uncertainty Based Scheduling• Experiments
– comparison to FullSearch– measurements on EVB80200 platform
• Summary & Conclusions
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Problem Set-up 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
s(1, ,k1) WCEii1
NAfref Xjj1
k1
E(X1, ,N ) X1K1s0 XiKii2
N s(1, , i1)
E(X ) E(x )xN
x1
(x1)(xN )dx1dxN
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A Motivational ExampleA Motivational Example
Task Set: 3 tasks, uniform distribution (BCE,WCE) = {1:(12,20),2:(10,30),3:(24,40)}A = 100, K=1, fref=1, =2
Execution Type
<1, 3, 2> 42.094 41.839 134%
<2, 3, 1> 37.482 36.978 119%
Ideal: always mean
31.443 (speed 0.68)
100%
Offline WCE 55.080 (speed 0.90)
175%
E[X]
E[X ]
E[X]%Ideal
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UBS in a NutshellUBS 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
E[X]
E[X ]
pubs(k) KkX k
s sk
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UBS vs. Full SearchUBS vs. Full Search
• 300 sets of each size(3,4,5,6 tasks)
• used the “real” E formula (4)
• under 2% difference
aa
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
2 3 4 5 6 7
% of No Scaling Avg. Energy
Task set size
UBSFull Search
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The Test Platform: EVB80200The Test Platform: EVB80200
•Intel i80200 (XScale)•MAX1855 voltage regulator•32MB SDRAM, 4MB Flash•RS232, JTAG, 7segLED
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UBS example on i80200: m6UBS example on i80200: m6
aa
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
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0
Power (W)
Time (s)
UBS (21.11mJ)Reverse UBS (24.34mJ)
Random (22.78mJ)WCE-stretch (28.58mJ)
MAX (37.57mJ)
• 6 tasks2 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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More Experimental Results: More Experimental Results: m6m6
0
5
10
15
20
25
30
35
40
45
0% 25% 50% 75%
Deadline extension
Hyp
erp
eri
od
En
erg
y (
mJ)
Max WCE-S R-UBS Rand UBS
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Experimental Results: m15Experimental Results: m15
0
5
10
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20
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0% 25% 50% 75%
Deadline extension
Hyperp
eri
od E
nerg
y (
mJ)
Max WCE-S R-UBS Rand UBS
5x LZ5x QS5x FOR
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Summary & ConclusionsSummary & 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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Measuring the core PowerMeasuring the core Power
aa
+-
9V470nF
470nF
diff
trimoffset
to Oscilloscope
LF351
Vcc
Vreg
3
2
Icc
U = Icc x 1
Vin = 10/11 Vreg
trim
9V
0.1
1k
1k
1k
5.1k
4.3k
51
4
7
10k
GND
CPU
-
+
-
+
-
+
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i80200 I/O Poweri80200 I/O Power
aaa
1. Assume system driving one PC-100 DIMM and a companion chip with 10pF/pin capacitance.
Bus Speed vs. Power (Moderat e BusUtilization)
0.00
0.10
0.20
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0.40
0.50
0.60
3.00 3.10 3.20 3.30 3.40 3.50 3.60
Vccp (Volts)
Pin Power (Watts)
66MHz bus
100MHz bus
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i80200 Core Poweri80200 Core Power
aa
Cor e P ower ( on Dhry st one 2 .1: h ig h c ore a c t iv it y )
0.000
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0.700
0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6Vcc (Volts)
Core Power (Watts)
400MHz
600MHz
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UBO extension to EDFUBO extension to EDF
• Use preemption to extract regions• Push forward uncertain regions• Algorithm:
1. Start from the latest deadline2. Between two consecutive deadlines order
the regions according to the already given priorities
3. Preempt the task which does not fit entirely4. Proceed with the next consecutive deadlines