soft-shake.ch - Optimizing iOS applications

Marc-Antoine Scheurer

Optimizing iOS applications

Agilité iPhone Java Incubateur

8:15 Accueil des participantsAccueil des participantsAccueil des participantsAccueil des participants

8:40 Mot des organisateurs & Criée des orateursMot des organisateurs & Criée des orateursMot des organisateurs & Criée des orateursMot des organisateurs & Criée des orateurs

9:00 Keynote de Nicolas Martignole (30 minutes)Keynote de Nicolas Martignole (30 minutes)Keynote de Nicolas Martignole (30 minutes)Keynote de Nicolas Martignole (30 minutes)

- A1 -Le terrain Agile

Jean-Philippe Vigniel

- I1-Hello iPhone

Stephane Tavera

- J1 -NOSQL also means RDF stores: an

Android case studyFabrizio Giudci

- X1 -Le développement durable

Dominic Williams

- A2 -Integration of User Centered Design

in Agile Development of RIAJ. Borkenhagen, J. Desmazières

- I2 -Développement d'une application

iPhone pilotée par les testsEmmanuel Etasse, Van-Charles Tran

- J2 -La Tequila du développement Web

Nicolas Martignole

- X2 -Cloud Computing: anatomie et

pratiqueMarc-Elian Bégin

- A3 -Adoption de l'Agilité par les usages

Xavier Warzee

- I3 -Distribution d'applications iPhone

en Entreprise: Réalisation d'un AppStore interne

Géraud de Laval

- J3 -Vaadin - Rich Web Applications in

Server-side Java without Plug-ins or JavaScript

Joonas Lehtinen

- X3 -Les DVCS sont vos amis

Sébastien Douche

Pause repas (50 minutes)Pause repas (50 minutes)Pause repas (50 minutes)Pause repas (50 minutes)

14h10 Keynote de Regis Medina (30 minutes)Keynote de Regis Medina (30 minutes)Keynote de Regis Medina (30 minutes)Keynote de Regis Medina (30 minutes)

- A4 - Scrum, introduction et mise en

oeuvre avec iceScrumClaude Aubry

- I4 -Agile iOS Development

Jérôme Layat, Alexander Osterwalder

- J4 -JAX-RS and Java EE 6

Paul Sandoz

- X4 -IT Design & Ergonomy

Pascal Petit, Aude Lussigny

- A5 -Agilité : 10 ans déjà

Thierry Cros

- I5 -Optimizing iOS applications

Marc-Antoine Scheurer

- J5 -Ecrivez et automatisez vos tests

fonctionnels avec jBehaveXavier Bourguignon

- X5 -NoSQL : Enfin de la biodiversité

dans l'écosystème des BDOlivier Mallassi

- A6 -Lean engineering

Jean-Christophe Dubail

- I6 -iPhone et Agile, l'amour vache

Guillaume Duquesnay

- J6 -Let's make this test suite run faster

David Gageot

- X6 -The feel of Scala

Mario Fusco

Mot de la fin & tombolaMot de la fin & tombolaMot de la fin & tombolaMot de la fin & tombola

Programme de la Conférence

www.soft-shake.ch

Optimizing iOS Applications

Marc-Antoine Scheurermarco@sente.ch

Optimizing is...

• Risky: “If it ain’t broke, don’t fix it”

• A hardware problem: “Buy a faster computer”

• Time consuming: “I don’t have time for performance work”

• Complicated: “I don’t know where to start or what to do”

• For the user: better experience

• For you: beat the competition

• For the OS: watch out the watchdog

A Hardware Problem:Limited Resources

3G 3GS 4 iPadCPU ARM 11 ARM Cortex A8 A4 (Cortex A8) A4 (Cortex A8)clock 412 MHz 600 MHz 1 GHz 1GHz

L1 32 KB 64 KB 64 KB 64 KBL2 - 256 KB 640 KB 640 KB

GPUtriangles /

PowerVR MBX Lite0.6 M

PowerVR SGX5.2 M

A4 (PowerVR SGX)28 M ??

RAM 128 MB 256 MB 512 MB 256 MBavailable 40 MB 150 MB 400 MB ? 150 MB

Flashavailable

8 - 32 GB2 GB

16 - 32 GB2 GB

16 - 32 - 64 GB2 GB

Screen 480x320 480x320 960x640 1024x728More GPS Compass Gyroscope

Battery 6h on WiFi 9h on WiFi 10h on WiFi 10-12h video

Where to start?Measuring Performance

• Guessing often does not work

• Measure - Change - Measure

• Use measuring tools

Measuring Tools

• NSLog

• Instruments

• Simulator

NSDate *startTime = [NSDate date];... NSLog (@"Elapsed time: %.3f", -[startTime timeIntervalSinceNow]);

InstrumentsTool Introduced

Objective C 1988

Interface Builder 1988*

Xcode 1988†

Instruments 2007‡

† Project Builder, renamed Xcode in 2003‡ Shikari, Shark in 2002

* SOS Interface, 1984-1986 (LISP, Mac)

Instruments• Profiling tool

• CPU

• Memory

• CoreAnimation

• CoreData

• OpenGL

• Power

• etc.

Simulator

• Software simulator ≠ hardware emulator

Simulator 3G

i386 ARM

2.5 GHz 400 MHz

Unlimited memory 40 MB

• Measure and test on oldest supported device (3G)

• Simulator OK to check memory usage

Better user experience

1. Responsive application

2. No crash (or kill by the watchdog)

3. Save battery life

1. Responsive applications

• Faster code

• makes applications more responsive

• uses less power

• Animation

• Objective C

• C and ARM code generation

• Frameworks

• File system

Animation

• Demo

Animation

• Scrolling at 60 fps

• Reuse identifier

• Opaque views

• Reuse formatters

• UINib (4.x)

Objective C

• Blocks

• IMP caching

[array indexesOfObjectsWithOptions:NSEnumerationConcurrent passingTest:^(id obj, NSUInteger idx, BOOL *stop) { return [obj test:value]; } ]

• Demo

Objective C

C and ARM Code Generation

• Demo

C and ARM Code Generation

• ARM v6 (2G, 3G)

• ARM v7 (3GS, 4)

• -Os vs -O3

• Floating points: remove Thumb on v6

• Contiguous memory, shadow variables, etc.

Frameworks

• Foundation

• Accelerate

• Grand Central Dispatch

Foundation

• NSMutableArray, NSMutableString

• insert O(N), O(1) at begin and end

• NSMutableDictionary, NSMutableSet

• lookup O(1) with good hash function

• NSMutableIndexSet

• Store integers without NSNumber

Accelerate• ARM v6• Integer unit with 16 registers

• Hardware floating-point (VFP)

• 32 single precision registers

• 16 double precision registers

• ARM v7• Integer unit with 16 registers

• Legacy VFP support

• NEON: 16 128-bit vector registers

• Single precision floating-point uses NEON

• NEON can decode MP3 on 10MHz CPU

Accelerate

• Makes using VFP and NEON easy

• Demo

Accelerate

• 2000 APIs for hardware accelerated math

• vDSP (Digital Signal Processing)

• Fourier transforms

• BLAS (Basic Linear Algebra Subprograms)

• Matrix product

• LAPACK (Linear algebra)

• Solving system of linear equations

• Later? vImage, vForce, ...

Grand Central Dispatch

• Concurrent programming

• Multicore or single core

• Easier and lighter than threads

• Use to move long processes off the main thread

• dispatch_async()

• Demo

Grand Central Dispatch

File system

• Access to Flash memory is relatively slow

• Speed vary a lot from device to device

• For large files use memory mapped files+[NSData dataWithContentsOfMappedFile:]

• Long I/O off the main thread

File System• I/O of small amount of data:

• NSUserDefaults

• Property Lists

• NSArchiver

• I/O of large amount of data:

• Incremental formats

• Databases (CoreData)

Property Lists• Binary Format 2-3x faster than XML

• Use NSPropertyListSerialization

-[NSArray writeToFile:atomically:] -[NSDictionary writeToFile:atomically:] -[NSString writeToFile:atomically:encoding:error:]

NSData *data = [NSPropertyListSerialization dataWithPropertyList:dictionary format:NSPropertyListBinaryFormat_v1_0 options:0 error:NULL]; [data writeToFile:path atomically:YES];

• Slow:

• Fast:

NSArchiver

• Not an incremental file format

Database

• Use CoreData

• Do not import large quantity of data...

• Add object stores instead

Database Search

• Unicode string comparisons are expensive

• Use normalized derived attribute (without accents)

• Use <= and < instead of BEGINSWITH

• Prefer prefix searching

Database Search• Point de Vue app: 25’000 records

3G Before After

[[each name] rangeOfString:searchString options:(NSAnchored| NSCaseInsensitive| NSDiacriticInsensitiveSearch)].location != NSNotFound

[[each asciiName] hasPrefix:searchString ]

“l” 0.704 0.450

“la” 0.032 0.024

“lau” 0.010 0.008

“laus” 0.001 0.001

2. No Crash

Activity Watchdog

Maximum Allowed TimeMaximum Allowed Time

Launch 20 s

Resume 10 s

Suspend 10 s

Quit 6 s

Operation 10 min

Memory Watchdog“Jetsam”

• Watches memory pressure

• Issues low memory warning

• Instant termination of application

Memory

• No swap

• (but yes: virtual memory)

• Memory usage also impacts time

• allocation time,

• unloading of executable code, ...

Memory Usage

• Avoid

• spikes

• leaks

• abandoned memory

• zombies

Memory Spikes

• Be smart with autorelease

• Process large quantities of data in batches

• Nested autorelease pools

• Demo

Memory Spikes

Memory Leaks

• Allocated memory that is inaccessible

• Unbalanced retain/release

• Forget to release property’s original value

• Leaks Instrument examines heap for leaked memory, identify allocation

• Xcode: Build and Analyze

Abandoned Memory

• Wasted memory

• Accessible but never used

• Memory should not grow without bounds

• Detect with Allocation Instrument: “heap shots”

Zombies

• Messages send to deallocated object

• Detect with Zombies template

• or Allocations “Enable zombie detection”

• Simulator only

3. Energy

Energy (iPhone 3G)

• 3G, WiFi, Bluetooth, GPS: 2 W

• CPU + GPU: 800 mW

• Screen: 200 mW

Radios and sensors

• Network

• CoreLocation

• CoreMotion

Network

• Bandwidth usage impacts time and power

• Use compact protocols (JSON vs XML)

• 3G networks require phones stay in high-power state for a few seconds after last packet is sent or received

• Limit number of connections

• Do not poll

• Use compact data formats

WiFi & 2G

• Less power than 3G

• 3G > 2G > WiFi

• Allowed to idle immediately

• 2G much slower

CPU• Burst

• Do not poll, use events

• Accelerate: more power, less energy

with NEONwithout NEON

CoreLocation

• Use minimum required accuracy

GPS kCLLocationAccuracyBest

GPS kCLLocationAccuracyNearestTenMeters

WiFi kCLLocationAccuracyHundredMeters

Cell / WiFi kCLLocationAccuracyKilometer

CoreLocation

• distanceFilter

• how often you receive location changed notifications

• default: all changes, many events, high CPU usage

• stopUpdatingLocation

• when good enough accuracy, switch GPS off.

CoreMotion

• Same thing

• Turn sensors off when in background (4.x)

Energy diagnostics

Energy usage

• Works on

• 3GS

• iPod 2 & 3

Level Battery life

20 Less than 1 hour

10 About 10 hours

1 More than 20 hours

Measure on the go• Enable device

to collect data

• Import in Instruments

Summary

Instruments’ instrumentsCPU

Memory

File System

Core Data

Graphics

Energy

Instruments Wireless• Connect device with USB

• Hold alt while choosing target

• Choose wireless device

• Disconnect from USB

• All the time

Useful links

• Xcode Developer documentation

• Applehttp://developer.apple.com/iphone

http://developer.apple.com/videos/wwdc/2010/

• Developer forumshttp://www.iphonedevsdk.com/

http://stackoverflow.com

• Developer classesStanford iPhone Application Development (english, free) sur iTunesU http://deimos3.apple.com/WebObjects/Core.woa/Browse/itunes.stanford.edu.3124430053.03124430055

Sen:te (french, paying)http://www.iphone-class.com

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