Real-Time Systems, 2009 FallProject 2: Energy-Efficient Scheduling For Android Environment

Advised by Prof. Tei-Wei KuoTA: Po-Chun Huang (黃柏鈞 )

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Introduction

• From the previous assignment, we know how to control the power modes of the backlight device on the Android platform

• However, it is not trivial to simply turn off the backlight device when we do not need it, for the considerable time and energy overheads on power mode switching

• Don’t worry; in this assignment we will find a clever way to do this (since it is required )

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Some Quick Facts

• Power consumption of T-Mobile G1

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Configurations of Peripheral Devices

Reference: http://rockthearth.blogspot.com/2009/04/power-consumption-of-t-mobile-g1.html

!!

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What Will Be Done in This Assignment? (1/2)

• We will be given a task set T of periodic tasks ti, for i=1, 2,…, N

– All tasks arrive at time point 0– Tasks are sorted based on their periods (so pi <= pj iff i<j)

• Each task has a period pi, deadline di, and several operations xij (i=1…N; j=1…ni), each of which has the following properties:– Luminance uij: can be C, DL and DH, standing for Computation

(no display required), Display in Low light and Display in High light, respectively

– Length lij: lij=1, 2, …(setting the time unit to 3~4 seconds is a good choice)

• The requirements of a feasible schedule is those of a conventional hard real-time environment, plus– The operations of the same task must be scheduled in the

specified order– During the scheduled time of each operation, the back light

device must be adjusted to at least as bright as that specified as required Luminance

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What Will Be Done in This Assignment? (2/2)

• Energy issues– During each time unit, the backlight device at none(C), low

light display (DL), and high light display (HL) consumes EC, EDL, and EDH of energy, respectively• Of course we can assume that EDH>EDL>EC>=0

• For simplicity we assume that EC=0

– Additional energy ESW is consumed on power level switching• For simplicity, we assume that switching from an arbitrary power

level to another demands the same quantity of energy• For simplicity, we assume that power level switching happens

immediately

• Our goal: Compute the feasible schedule with minimal energy consumption!

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A Sample Input

• The input will be given to you manually; you can hard-code them in your sources (with clear mark so that I know it’s the input )

• T = {t1, t2, t3}– t1 = (16(p1), 14(d1), ((1, 0(C))(x11), (1, 1(DL))(x12)))

– t2 = (20(p2), 20(d2), ((1, 2(DH))(x21), (3, 1)(x22)))

– t3 = (28(p3), 20(d3), ((1, 0)(x31), (1, 1)(x32), (1, 0)(x33)))

– EC=0, EDL=1, EDH=5, ESW=12

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Scoring

• Baseline: RM schedule (30%)• Implement then write down your improvement

over the RM schedule in reports (70%)– Must provide the intuition and sufficient examples to

show why it is better than original RM!– Must output the detailed computed schedule with

LogCat!

• Better if you can prove the bound of energy or time! (30% bonus)

• Even better if you can compose a demo of your algorithm on the Android emulator! (30% bonus)

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The LogCat Debugging Console

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Open the LogCat Console View

• Add the LogCat view to menu shortcut: Window -> Customize Perspective -> Shortcuts -> Submenus : Show View -> Categories : Android -> LogCat

• Open the view: Window -> Show View -> LogCat

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Print Customized Debugging Messages in LogCat• Import android.util.Log package in your project

• Use the static variable Log to keep trace of your target: Log.d("DEBUG", "message");

• Please use the message typed “DEBUG” to make them distinguished from system messages!

• You should print at least the following messages:– If the task set is un-schedulable, simply print “Unschedulable!”– Else, during the time interval [0, LCM(p1, …, pN)), in each time unit, the light

level and the IDs of scheduled operation and its residing task should be printed as: Time XX: Running task XX, operation XX, H(high light)/L(low light)/N(no light)

– If nothing is being executed during that time, print: Time XX: Idle, H/L/N– By the end of program, print out a summary message about the total energy

consumption statistics, and the number of light level switching, using RM and your algorithms respectively:Total high light time: XXTotal low light time: XXTotal no light time: XXTotal light switching: XX timesTotal energy consumption of my algorithm: XX

– Finally print the degree of improvement: Energy improved by 17%

• You should include this result of each of the 5 test cases in your report! For the test cases please see the web site.

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Sample Outputs 1

• ---- RM ----– Unschedulable!

• ---- My program ----– Unschedulable!

• ---- Results ----– Unschedulable!

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Sample Outputs 2• ---- RM ----

– Time 0: Running task 1, operation 1, H– Time 1: Running task 2, operation 1, L– ……– Time 48: Running task 1, operation 1, N– Total high light time: 22– Total low light time: 15– Total no light time: 11– Total light switching: 16 times– Total energy consumption: 130

• ---- My program ----– Time 0: Running task 1, operation 1, H– Time 1: Running task 1, operation 2, H– ……– Time 48: Running task 2, operation 1, N– Total high light time: 17– Total low light time: 16– Total no light time: 15– Total light switching: 6 times– Total energy consumption: 108

• ---- Results ----– Energy improved by 17%

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Hint 1: Modify RM

• Modify RM to reduce power without sacrificing schedulability

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Hint 2: Idle Time…

• How about the light mode between scheduled task operations?

• We know that• How about… H H???

H L???

L H???

N NN

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Hint 3: Moving and Swapping

• Moving: Without violating the deadlines, move the scheduled points of tasks left or right to reduce the idle time

• Swapping: Without violating the deadlines, swap the scheduled points of tasks to reduce light level switching L H L H

L HL H

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Hint 4: Switching the Power Levels based on the Schedule

of Your Solution• Thread.sleep lets a thread “sleep” for a

specified time period• Thread.run executes the thread’s method

• Thread.join waits for the created thread

to finish for its computation results

• No need to create a thread for each

task…

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Submission• The deadline of this assignment is 1/7,

23:59• Mail to f95070@csie.ntu.edu.tw with

– Title: [RTS Project II] Your-Student-ID Your-Name– Attached files:

• Project directory compressed into a single file: Your-Student-ID.zip/.tar/.tgz/.7z

• Report: Your-Student-ID.txt

– You will receive a confirmation about your submission in two days; if not, please contact TA immediately

– Any questions are welcome through E-mail or face-to-face discussion in R442!

Q&A?Thank You!

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