How to lower the power consumption of

your app, without affecting performance

Rick Schwartz

Qualcomm Technologies, Inc.

developer.qualcomm.com

mostly-tech.com

About this session

• Most mobile apps do not use the processor, cellular radio

and other system resources efficiently

• This wastes power, which has a negative effect on battery

life

• It’s easy to measure power consumption. If you can

measure it, you can act on it

• Solutions to common power problems are readily available

• Better battery life = happier users

Battery life really matters

Why long battery life is such a challenge

Hardware specs have increased dramatically, but batteries have not

Source: Samsung.com/us website

Samsung Galaxy SIII

Samsung Galaxy S6

So, where does the power go?

Source: Android Power Profile for the Nexus 6 smartphone. Data provided by device manufacture. Current converted to power

#1

#3

#2 CPU

#4

#5

#6

How to get a power profile for any phone

• Read up on Android Power Profiles: https://source.android.com/devices/tech/power/index.html

• Where to find one on your device: platform/frameworks/base/core/res/res/xml/power_profile.xml

• There’s also an app for this

• Values are displayed in current

P = I x V (battery voltage)

Power Profile app on Google Play

How much power does your app consume?

Measuring power using Trepn™ Profiler

Launch Trepn, go to Settings

and select Battery Power

Check “Acquire Wakelock to

keep the processor awakeSelect an app to profile

1 2 3

Source: Trepn Profiler screenshots. Trepn is a product of Qualcomm Technologies Inc.

Measuring power using Trepn Profiler

Source: Trepn Profiler screenshots. Trepn is a product of Qualcomm Technologies Inc.

4 Select how to view the power data

Other software options are available

Android 5.0 Battery app GSam Battery Monitor Pro GameBench Power Tutor

If you can measure it, you can act on it

• First, measure the power of your device idle with the

screen on and off

• Next, measure the average power of your app when it’s

idle and in-use

• Compare the power consumption of your app to other

similar apps

• Try different things:

- Does code A or code B consume more power?

Inserting markers into your code

Trepn Profiler’s application states help identify the cause of power spikes

Step 1: Insert application state markers into your code

Step 2: Look for spikes in Trepn’s graph view. Determine which section of code they occur in

Source: Trepn Profiler 5.0 screenshots

Step 3: Make changes to your code, and look at the average

power readings for each state in Trepn’s Stats view

Reading the power consumption from the power management IC results in a strong

correlation between system resource usage and the power used

Source: Trepn Profiler 5.0 running GLBench

The advantage of direct power measurement

Are software power measurements accurate?

The chart shows how Trepn’s power readings compare to a Monsoon Power Monitor

Source: Qualcomm internal power measurements of a Nexus 6 running Trepn software at various screen brightness levels

How to perform automated testing

A simple example how this can be done

Source: Trepn Profiler 5.0 screenshot

Making intelligent decisions

Source: Trepn screenshots of Nexus 5 running MX Player

Video playback using S/W decoder Video playback using H/W decoder

43% less power consumedAlmost 3x more CPU load

Trepn shows how much power is saved when using hardware decoding

Pros and cons of software and hardware power

measurement

Software Power Measurement

• Much easier – Doesn’t require modifications to the battery or phone

• More portable – Doesn’t require a cable connection; Supports mobile use

cases

• Capable of per-rail power measurements for hardware blocks

• Not every device supports direct power measurement

Hardware Power Measurement

• More accurate - Off-target, so it doesn’t consume processor cycles

• Often provides more detailed and customizable graphs

• Misses less spikes - Capable of higher sample rates

Measuring per-rail power consumption

Snapdragon development tablets are available from

• The Snapdragon 805 (8084) MDP displays power for the CPU, Camera, Digital Core, GPU,

Internal Memory, LCD Backlight, SD Card and WLAN/Bluetooth

• The Snapdragon 810 (8994) MDP displays power for the CPU Cores 0-3, CPU Cores 4-7,

GPU, LCD Backlight, Front Camera, Rear Camera, System Memory, Internal Memory/SD

Card, Wi-Fi/Bluetooth, Sensors and USB

Power delta before photo taken Power delta after photo takenSource: Trepn Profiler 5.0 screenshots

Qualcomm Snapdragon is a product of Qualcomm Technologies, Inc.

1. Direct connection to the battery

contacts via mini-grabber cables

2. Using flat insulated copper tape

3 different ways to connect your device to

power measurement hardware*

3. Circuit board modification

Sources: Nexus photos taken by the authorNote: Any connection to power measurement hardware is done at your own risk

Power Measurement Best Practices

1. Remove your USB cable – You cannot display accurate power readings when your

mobile device is charging or connected to a computer. Tip: Use ADB over Wi-Fi

2. Make sure the CPU in the device capturing the power data stays awake

3. Minimize background processes – Open the Apps manager, go to Running and close

all remaining unneeded apps and stop all unneeded services

4. Focus on what you’re measuring – Turn off everything that is not related to what

you want to measure (e.g., Wi-Fi, Mobile networks, Location (GPS), Bluetooth,

Google Now, etc.)

5. Minimize the impact of the screen – The screen is the biggest consumer of power.

Turn the brightness down to the minimum possible level or turn it off

6. More power measurement Best Practices are available here

Does your app have a power problem?

The Top 5 power problems

Does your app use the cellular radio efficiently?

Many apps don’t use the cellular radio efficiently

Multiple apps acting independently creates

network signaling congestion

• Apps pull notifications, updates and message users -

- even when a phone is not being used

• Most news and social networking apps wake up your

device at least four times an hour

Source: The Smartphone Challenge: Signaling Congestion and Power Consumption - Gerardo Giaretta - Qualcomm

Why is this a problem?

• A dormant cellular radio consumes

about 10-12 mA

• When data is sent or received, the

radio comes up and goes into an

active state, consuming 250-350mA

• When not sending data, the radio

drops down to idle, but still

consumes about 30mA to 150mA

• After a timeout of 8 to 15 seconds,

the radio finally goes back to a

dormant state

Source: Qualcomm Technologies Inc. internal testing

Is your app is using the cellular radio efficiently?

Use AT&T’s Application Resource Optimizer (ARO )to find out

You can download it here: https://developer.att.com/application-resource-optimizer/get-aro

Source: Screen image used with permission

What else can you do with ARO?

• Collects traces from a test device or Android emulators

• Provides detailed recommendations how to fix problems

• Open-source code can be integrated into automated test suites

Source: Screen image used with permission

ARO Test Results

Screen images used with permission

Real world cellular radio power consumption

1. Radio goes from idle to transmitting

- Power increase >800mW

2. Radio back to idle

- Power decrease >800mW

3. Radio goes from idle to transmitting

- Power increase >1200mW

4. Radio goes from idle to transmitting

- Power increase >600mW

5. Radio goes from idle to transmitting

- Power increase <500mW

6. Radio goes from idle to transmitting

- Power increase <500mW

7. Radio goes from idle to dormant

- Power decrease ~600mW

8. Radio goes from idle to transmitting

- Power decrease ~500mW

1 2 3 4 5 6 7 8

Source: Qualcomm Technologies Inc. internal testing using Trepn Profiler to graph the

mobile data states of a Nexus 7 with LTE accessing data from Google Drive

Charts make it easier to correlate actions with

system resource consumption

Source: Trepn plug-in for Eclipse running on an active Samsung Galaxy Note 3

Don’t forget to check idle behavior

All 4 cores are active here

GPU active here

250mA to 350mA of power is used here Even though the cellular radio is idle, it still consumers up to 150mA of power

GPS active here

Wi-Fi active here

Source: Trepn plug-in for Eclipse running on an idle Samsung Galaxy Note 3

Make changes and see the impact

Mobile data transmitted before Google Now turned off

Mobile data transmitted after Google Now turned off

Google Search app

Source: Trepn plug-in screen excerpts

Small changes can make a big difference in cellular radio usage

How to efficiently use the cellular radio

How to efficiently use the cellular radio

1. Connect less often – After you transmit the radio stays on for 10+ sec1

2. Push, don’t poll – Send packets and wait to see if they respond. Use

the Google Cloud Messaging system (GCM) API instead. Have it send you

data when things have changed. Specify how often items are delivered2

3. Don’t continuously scan1

1. Create timeouts appropriately when scanning for Wi-Fi networks or GPS signals

4. Offer ad-free versions – Apps without ads connect to the network much

less often

5. Use analytics wisely1

1. Capture data locally and group transmissions to your server. Extend the time

between transmissions

1 Source: AT&T “Tips to Increase Battery Life Handout” from AnDevCon 20132 Source: Google Developer Advocate Colt McAnlis at from “Efficient battery use on mobile” at “Perf Like a Pirate.”

Analytic and ad services vary greatly

Source: Data provided by Crittercism

Error rates and response times by top services

Findings• Google Analytics has lowest error

rate (0.1%); error rate is percent of

errors per number of service calls

made

• Of top public services, Google

Analytics has lowest average latency

Takeaway• Even top services like Google

Analytics and Facebook experience

latency and error rates

• Teams must manage every aspect of

mobile app performance, including

third-party services

Follow the leader(s)

BBC News App (23 SDKs) BBC website (38 SDKs)Source: Data provided by MixRank

See which SDKs popular apps and sites useApache Commons ChartBeat

Simple Logging Façade for Java Facebook Open Graph

Android Volley Adobe Analytics/Omniture

OpenUDID Bing Webmaster Tools

Omniture Effective Measure

17,289 7,87329,386 46,675

12,475 4,47225,905 38,380

9,166 5,1414,285 13,451

3,296 1,3996,657 9,953

1,196 396794 1,990

Current installs Uninstalls Total installs Developers

Current installs Uninstalls Total installs Developers

Current installs Uninstalls Total installs Developers

Current installs Uninstalls Total installs Developers

Current installs Uninstalls Total installs Developers

36,641 189K Dec 4, 2013

5,880,253 402K

224,454 1M

813,284 109

8,735 975K

Websites Times Seen First Seen Last Seen

Websites Times Seen First Seen Last Seen

Websites Times Seen First Seen Last Seen

Websites Times Seen First Seen Last Seen

Websites Times Seen First Seen Last Seen

May 12, 2015

Jan 29, 2012 May 12, 2015

Jan 29, 2012 Apr 20, 2015

Apr 10, 2015

Apr 10, 2015

Jan 29, 2012

Jan 29, 2012

How to efficiently use the cellular radio

6. Don’t continuously stream – Download streams in chunks1

7. Use the JobScheduler APIs that are part of Android 5.02

1 Source: AT&T “Tips to Increase Battery Life Handout” from AnDevCon 20132 Google I/O 2014 - Introduction to Project Volta by (Meghan Desai and Matthew Jay Williams)

Before

After

Bundling traffic reduces overhead-to-data ratio

Source: The Smartphone Challenge: Signaling Congestion and Power Consumption - Gerardo Giaretta - Qualcomm

Use Battery Historian to view wakelocks & radio usage

One-time setup in order to run Battery Historian

1. Download and install Python 2.7 (if it’s not already installed)

2. Download battery-historian from GitHub

3. Extract “historian.py” from the zip file and copy it to the Python2.7 directory

Running Battery Historian

Type the following into the command prompt after connecting to an Android 5.x device:

How to efficiently use the cellular radio

6. Wait for the right connection – Avoid sending packets on slow

cellular connections. Wait until you are on Wi-Fi, if possible.

Some apps provide users with

the option to only upload when

charging. Choice is good.

Source: Microsoft OneDrive screen capture

Why should you wait for Wi-Fi?

Source: Qualcomm tests. Monsoon power measurement from a download of 3 apps

over a 1-2 bar 3G/4G cellular connection using a Verizon Galaxy Note 3

More power is consumed

• Power before download 723 mW

• Power during download 3279mW

• Radio power use: ~2556mW

• Downloading large files over

Wi-Fi consumes less than half

the power

• Estimated battery life dropped

from 15.8 hours to 5.1 hours

Mobile data wasted: 67.68MB

Time wasted: 11 minutes

Downloading data over a cellular radio with a

weak signal requires more power

Does your app keep the processor awake?

33

How to tell if your app keeps the processor from

going to sleep?

Using Wakelock Detector (WLD) to identify processor sleep problems

CPU Wakelocks Wakeup Triggers

• A recent study found that 23% of apps have problems with wakelocks. This can drain the battery of an inactive handset in as little as 5 hours

• Wakelocks do have a place, because your processor goes to sleep when it’s idle. Apps need wakelocks for alarms, GPS location and to wake up the processor to check for new messages.

An easy way to spot excess resource consumption

Processor stats can be viewed by going to Settings > Battery and

selecting your application

Source: Android 5.0 battery stats screenshots

If your app is not in the foreground, there should be a good reason why it’s keeping the processor awake and consuming data

How to avoid keeping the processor awake

1. Do not acquire PowerManager.Wakelocks unless you really need them

Battery life will be significantly affected by the use of this API

• Use the minimum levels needed

• Release wakelocks as soon as possible

2. Consider using AlarmManager in situations when you want to have your

application code run at a specific time

• Beginning with KitKat, the OS shifts alarms to minimize wakeups and

battery usage

3. For normal timeouts, it’s easier and more efficient to use Handler

Does your app manage the display in a power

efficient manner?

Managing display power efficiently

1. Full wakelocks keep your screen from turning off.

To keep the display lit when your app is in the

foreground, use FLAG_KEEP_SCREEN_ON

2. There is a direct correlation between screen

brightness and power consumption

3. Offer a dark theme option. Gray or black

backgrounds consume less than half the power of

a white background

Source: Qualcomm average power measurements using a Monsoon Power Monitor of the Google New & Weather app on a Samsung Galaxy Note 3 with the display at 50% screen brightness

Source: Qualcomm tests of Nexus 6 average power consumption using a Monsoon Power monitor

Does your app use all available system resources?

Some apps don’t use resources efficiently

Source: Trepn Profiler 5.0 screenshots

Is your app CPU bound or GPU bound?

Source: Trepn Profiler 5.0 screenshots

Does it use all available CPU cores?

Source: Trepn Profiler 5.0 screenshots

Heterogeneous computing is key

Run the right task on the right processing engine

Source: Qualcomm internal power tests using QEPM software eQualcomm SeeMore demo using the MARE SDK

a product of Qualcomm Technologies, Inc.

Qualcomm Multicore Asynchronous Runtime

Environment

MARE is a developer programming library, API and runtime system for heterogeneous programming

How to save power by offloading to DSP

Benefits of offloading to DSP

• Extends music playback time to 60 hours. A 50% increase.

• When batching sensor data, 8 hours of sleep tracking only

uses 10 to 20% of available battery life

• Running FastCV™ facial detection on DSP instead of the CPU

uses 32% less power

1. Audio playback done using a Nexus 5 using Bluetooth headphones and the display off.

2. Sensor batching done on Samsung Gear Live with Sleep as Android app

3. Power measured at the device battery. Source: Qualcomm Technologies Inc. internal measurements

Does your app take too many GPS fixes?

How to save power when using the GPS

1. Make sure you don’t take a GPS fix when

it’s not needed

2. Use coarse GPS fixes when possible,

because they require less power

3. Let LocationManager find the best provider

4. Have a timeout if you can’t find a satellite

5. Disable GPS when your app sleeps to save

power

6. Make it easy for users to disable location

tracking without crippling their deviceSource: Android 5.0 Location Settings on Samsung device

Perf Matters Too!

Use tools like these to confirm your perf hasn’t changed

• ARM Streamline, GameBench, Adreno Profiler, Trepn

Profiler, PerfMon, Intel INDE or Qualcomm® Snapdragon™

Profiler

Real-time or post-capture viewing

and analysis of a wide range of

system and app level power,

performance, thermal and

network usage metrics

Coming Soon: Snapdragon Profiler

Qualcomm Snapdragon and Qualcomm Adreno are products of Qualcomm Technologies, Inc.

Recap of power saving tips

• Use wakelocks only when necessary

• Close TCP sockets when done. Otherwise, you unnecessarily bring up the network just

to tear down. This simple fix can reduce network power up to 20%

• Group network activity when possible

• Keep performance headroom for additional power savings. Saves significantly in overall

system power.

- Optimize your app to run at 60fps, but then frame-rate limit it to lower rate (ideally

30fps). This cuts GPU, CPU and memory utilization and hence related power by 50%.

Also guarantees smooth consistent UX flow at same framerate

• Avoid rendering at full native display resolutions. This saves GPU power.

- Test rendering applications at lower resolutions

- Games should ideally render at 1080p or lower resolutions natively

@YourTwitterHandle#DVXFR14{session hashtag} @mostlytech1#powermatters

Helpful mobile power-related links

• Software power measurement best practices – Rick Schwartz

• Hardware power measurement best practices – Rick Schwartz

• Battery Drain and Networking – Colt McAnlis

• What These Apps Did May Shock You - Doug Sillars

• Understanding Battery Drain on Android – Colt McAnlis

• How to power profile an app using hardware – Rick Schwartz

• Battery Drain and WakeLocks – Colt McAnlis

• AT&T Application Resource Optimizer demo - Doug Sillars

• Monsoon Power Monitor - Tips & Tricks – Rick Schwartz