1. EnTrack: A System Facility for Analyzing Energy Consumption of Android System Services

2. Background Energy efficiency is a critical issue for mobile device.
Energy accounting is essential for developing energy-efficient applications.
Previous studies consider the energy consumption of an application as the summation of the energy consumption of the constituent processes(the processes and threads with the same UID).
Such energy consumption methods are not accurate when considering system service!

3. Energy Models
22.2% of energy consumption is attributed to System Processes

4. Innovations
Tracking the relationship between applications and services
Providing fine-grained energy consumption of system services according to function unit
Accounting the energy consumption of applications linked with system services.

5. EnTrack Architecture

6. Service Tracer Binder Tracer Interaction Identifier
Hook into Binder Driver [jprobe]
Acquire IPC message
Interaction Identifier
Analyze data from Binder Tracer
Interaction Data Manager
Maintain a caller list of system service
Framework Tracer
Deal with location & graphics processing

7. Framework Tracer

8. HW Usage Accounter & Application Energy Analyzer
Hardware Usage Accounter
Collect hardware usage information
The same way as AppScope
Application Energy Analyzer
Process-level energy consumption
CPU and network energy consumption
The same as AppScope
Disaggregate energy consumption of system service to the caller
Decompose energy consumption at GPU according to the display proportion
Decompose energy consumption at GPS equally to applications which use GPS concurrently

9. Evaluation: Accuracy & Functionality
Service Tracker
Hardware Usage Accounter
Add code to log service usage information
Execute five applications both sequentially and simultaneously.
Rerun the scenario and collect data with EnTrack
A margin of error of 4.94%
Compare the monitoring results: exactly the same

10. Evaluation: Accuracy & Functionality
Application Energy Analyser

11. Evaluation Analysis Capability Overhead CPU Utilization: 1.8%
Memory Overhead: Rather High
Log size of 450-second scenario: 581 KB

12. Case Study 1: LBS Application
Two versions of a LBS application:
Old version: use AlarmManager to activate GPS sensor and it consumes most energy.
New version: use Handler instead of AlarmManager to activate GPS sensor.

13. Case Study 2: Web Browser Optimization
Tab Switching Optimization:
Overall energy usage decreased from 90,000mJ to 65,800mJ
Version 25.0:
Load the images in all web pages
Version 26.0:
Only load images visible to the user

14. Case Study 3: Energy Bug of Web Browser
Firefox continues to operate the timer or video when the application runs in the background.
EnTrack tracks the energy consumption with the android.hardware.IOMX system service in the Media Server.
android.hardware.IOMX continuously consumes a certain amount of energy although the application does not consume energy for display.

15. Conclusion
EnTrack keeps track of interactions between application and system service and disaggregates energy consumption of system services to each application.
Evaluation shows that EnTrack improves analysis capability of energy consumption compared with the existing method.
The case studies show that EnTrack can be used as a developer tool for energy optimization.
The limitation of EnTrack is that the energy consumption used by the kernel is not considered.