soft-shake.ch - Optimizing iOS applications

Marc-Antoine Scheurer
2010
i5
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)
9:40
10:40
- A1 -
Le terrain Agile
Jean-Philippe Vigniel
- I1-
Hello iPhone
Stephane Tavera
- J1 -
NOSQL also means RDF stores: an
Android case study
Fabrizio Giudci
- X1 -
Le développement durable
Dominic Williams
11:00
12:00
- A2 -
Integration of User Centered Design
in Agile Development of RIA
J. Borkenhagen, J. Desmazières
- I2 -
Développement d'une application
iPhone pilotée par les tests
Emmanuel Etasse, Van-Charles Tran
- J2 -
La Tequila du développement Web
Nicolas Martignole
- X2 -
Cloud Computing: anatomie et
pratique
Marc-Elian Bégin
12:20
13:20
- 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)
14h50
15h50
- A4 -
Scrum, introduction et mise en
oeuvre avec iceScrum
Claude 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
16h10
17h10
- A5 -
Agilité : 10 ans déjà
Thierry Cros
- I5 -
Optimizing iOS applications
- J5 -
Ecrivez et automatisez vos tests
fonctionnels avec jBehave
Xavier Bourguignon
- X5 -
NoSQL : Enfin de la biodiversité
dans l'écosystème des BD
Olivier Mallassi
17h30
18h30
- 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

© Copyright 2010, Sente SA.All rights reserved. http://www.sente.ch
Optimizing iOS Applications
marco@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”

Why?
• 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 iPad
CPU 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 KB
L2 - 256 KB 640 KB 640 KB
GPU
triangles /
s
PowerVR MBX Lite
0.6 M
PowerVR SGX
5.2 M
A4 (PowerVR SGX)
28 M ??
A4 (PowerVR SGX)
28 M ??
RAM 128 MB 256 MB 512 MB 256 MB
available 40 MB 150 MB 400 MB ? 150 MB
Flash
available
8 - 32 GB
2 GB
16 - 32 GB
2 GB
16 - 32 GB
2 GB
16 - 32 - 64 GB
2 GB
Screen 480x320 480x320 960x640 1024x728
More 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

NSLog
NSDate *startTime = [NSDate date];
...

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

Instruments
Tool 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

Time
• Faster code
• makes applications more responsive
• uses less power

Time
• 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
• LegacyVFP support
• NEON: 16 128-bit vector registers
• Single precision ﬂoating-point uses NEON
• NEON can decode MP3 on 10MHz CPU

Accelerate
• Makes usingVFP 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 deVue 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
• 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
Power
Time
with NEON
without 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
• 4
• 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’ instruments
CPU
Memory
File System
Core Data
Graphics
Energy

Instruments Wireless
• Connect device with USB
• Hold alt while choosing target
• Choose wireless device
• Disconnect from USB

When?
• All the time

Useful links
• Xcode Developer documentation
• Apple
http://developer.apple.com/iphone
http://developer.apple.com/videos/wwdc/2010/
• Developer forums
http://www.iphonedevsdk.com/
http://stackoverﬂow.com
• Developer classes
Stanford 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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