Tips and Tricks: Designing low power Native and WebApps. Harita Chilukuri and Abhishek Dhanotia

Transcription

1 Tips and Tricks: Designing low power Native and WebApps Harita Chilukuri and Abhishek Dhanotia

2 Acknowledgements William Baughman for his help with the browser analysis Ross Burton & Thomas Wood for information on Tizen Architecture Tom Baker, Luis Fernando Recalde, Raji Shunmuganathan and Yamini Nimmagadda for reviews and comments 2

3 Power Onus lies on Software too! Use system resources to provide best User Experience with minimum power NATIVE APPS WEBAPPS RUNTIME Interfaces with HW components, Independent device power management Frequency Governors, CPU Power Management ACPI/RTPM Provides features for low power Clock Gating, Power Gating, Sleep States DRIVERS / MIDDLEWARE OS HARDWARE 3

4 Power Onus lies on Software too! A single bad application can lead to exceeding power budget Hardware and OS provide many features for low power Apps need to use them smartly to improve power efficiency Good understanding of underlying system can help in designing better apps 4 Images are properties of their respective owners

5 Agenda Power Tools & Metrics Tips for Low Power Applications General guidelines Q&A 5

6 Estimating Power - Metrics CPU utilization Memory bandwidth CPU C and P state residencies Device D states - For non-cpu components S states system sleep states Wakeups, interrupts Soft metrics can help tune the application for optimal power 6

7 Estimating Power - Tools CPU utilization Vmstat, Top VTune, Perf for CPU cycles Memory bandwidth Vtune CPU C and P states, Device D states VTune, Powertop Wakeups, Interrupts, Timers Powertop, /proc stats Tracing tool in Chrome browser ** VTune is an Intel product and can be purchased, others are publicly available Linux tools 7 * Other names and brands may be claimed as the property of others.

8 Tip 1: Minimize wakeups, they are expensive 8

9 Power (mw) Tip 1: Minimize wakeups Classic case of a single application exhausting the power budget Wakeups from each app add up Even if its just 0.5 wakeups/sec wakes 80wakes 60wakes 40wakes 20wakes 10wakes 1 wakes Total system wakeups from all applications 9

10 Power (mw) Battery Life (hrs) Tip 1: Minimize wakeups 1400 Polling, Frequent I/O Timers Wakeups/sec Power Battery Life Background Activity

11 Tip 1: Minimize wakeups How to reduce wakeups - Polling - High frequency timers - Avoid frequent I/O + Maximize the work done when the system wakes up, batch operations + Longer sleep time is better than frequent shorter sleep times Apps accessing data from peripheral components/sensors GPS, Games using accelerometer etc. Apps doing periodic updates Push notifications instead of polling 11 Images are properties of their respective owners

12 Tip 2 Use Hardware Acceleration 12

13 CPU C0 % Tip 2: Use hardware acceleration 120 HW Overlay and Rendering in GPU Decoding in Audio Engine Compositing in GPU Video Playback Audio Playback HTML5 Video Webapp SW based functions HW Accelerated functions 13

14 Tip 2: Use hardware acceleration Caveats Benefits from acceleration vary based on use case HW Acceleration improves performance only when TIME (memcpy + work in HW) < TIME (work in SW) Power Software Hardware Acc CPU GPU Memory 14

15 Tip 2: Use hardware acceleration Common formats that are usually accelerated or optimized Developers should use these when applicable Video Audio Browser MPEG2 MP3 GPU Accelerated Compositing MPEG4 AAC GPU Rendering H264 EGL VC1 Media apps, local playback and streaming Games 15 Images are properties of their respective owners

16 Tip 3: Don t shoot for performance beyond what a user can perceive 16

17 Tip 3: Performance Vs. Power Tradeoff Video playback power use with different frame rates ~2.5x increase from fps FPS = 15 FPS = 30 FPS = 45 FPS = CPU% Power * Power here is the difference between system idle and video playback, data normalized to 30 fps. 17

18 Tip3: Performance Vs. Power Tradeoff Trying to maximize performance without knowledge of user expectation + Make a tradeoff Media Apps Videos beyond 30 fps are rarely perceivable on mobile devices Audio bit rates beyond audio HW output capacity won t sound better Games Screen refresh rates are 60/120Hz, frames are dropped beyond that 60 fps may be overkill for some applications 18 Images are properties of their respective owners

19 Tip 4: Minimize Latency & JavaScript 19

20 SOC Power (Watts) Tip 4: Minimize Latency & JavaScript Server latency = 138ms Server latency = 1.2s Time Google Search Ask Search Average SOC power for Google search is 919mW, for Ask search, its 1031mW, ~10% difference 20

21 SOC Power (Watts) Tip 4: Minimize Latency & JavaScript JavaScript, Issue more requests to different domains Time Google Search Ask Search 21

22 SOC Power (Watts) Tip 4: Minimize Latency & JavaScript Receiving more data Time Google Search Ask Search 22

23 Tip 4: Minimize Latency & JavaScript + Batch requests + Cache external resources - Many sequential connections - Long latencies Ask batches some requests, but not all. Web Applications 23 Images are properties of their respective owners

24 Tip 5: Minimize Comm. Power 24

25 WiFi Power (watts) Tip 5: Minimize comm. power Difference in server response latencies causes wider active time for Wifi Time ASK Wifi Google Wifi 25

26 WiFi Power (watts) Tip 5: Minimize comm. power Data Request => Active Connection => Wide Wifi Power Wakeups => More Power Time ASK Wifi Google Wifi 26

27 Tip 5: Minimize comm. power How can you reduce Wi-Fi power consumption? + Batch processing - Long latencies Web Applications 27 Images are properties of their respective owners

28 Some other general guidelines for low power Context awareness Minimize system resource use when not in foreground Subscribe to screen and other system events Free up temporary cache, files, and images Clean idle Use resources only when user is active Only act on user input does piggybacking or deferring tasks to the next system wakeup work? The power profile of an idle app should match system idle Idle system CPU utilization target is less than 1% 28

29 Summary Battery life is an important selling factor Keep power in mind from Day 0 of development Follow our tips to make a good app-world citizen Enjoy Developing Green Apps! us at harita.chilukuri@intel.com & abhishek.dhanotia@intel.com 29

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