Project “Smoke”N-core engine experiment

Threading for PerformanceAND Features

“Smoke” is threaded for performance and features – here’s how!

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•Well partitioned, configurable

•Share source, demos, samples, workloads, white papers

•More info at Intel Developer Forum

Engine + framework with typical game subsystems

Experiment with game tech – how does it all fit together?• Explore performance on n-cores

– Framework designed to scale to n threads– Which game architecture runs well with 8

threads? More?• Try features

– Procedural fire/smoke– Dynamic vegetation, etc.

• Measure them separately/together (to see interplay)– Core threading techniques– Physics– Dynamic vegetation– Fire/smoke, etc.

• Extend into the future

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It’s working today!

•Display (Ogre3D)•TaskManager•Physics•Sound•Volumetric Smoke•Procedural Fire•Procedural Trees•AI•Animation•User input/control

•Scripting•Instrumentation•Camera bot

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The framework holds it together

Heavy use of interfaces, easy to extend

Minimizes thread sync via messaging

Most of the code is in the Systems

EngineManagersFramework

Scheduler Parser Environment

Service

Platform

TaskMessaging (Change control)

UScene

UObject UObject…

Systems

Definition Files

Interfaces

System

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GDC 2007: Restructuring will take games to multiple processors!

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Three configurations:• Single thread – shut threading off• Native threads• Threading Building Blocks

Thread count scales to HW (4-core here)Task Manager puts System’s update in

poolSystems chunk the update for other

threadsThread pool used by all systems (even

external ones, like Havok)

Task Manager: scalable n-core thread pool

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AI System

Graphics System

Physics System

Systems subscribe to change messages

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• Each system subscribes to changes it needs

• Decoupled communication reduces dependencies– Observer/Mediator

• Lower memory bandwidth

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Subscribe

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AI System

Graphics System

Physics System

Physics Physics

AI

Render

AI AI AI ...

Tasks get subdivided

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•Scheduler invokes each system per frame

•System subdivides work into sub-tasks

•Using “natural” granularity

•Good middleware makes this easy

AI System

Graphics System

Physics System

Physics Physics

AI

Job Pool

Render

AI AI AI ...

Render

Physics Physics

AI AI AI AI ... 10

Tasks get subdivided

•All sub-tasks in single job pool

AI System

Graphics System

Physics System

Physics Physics

AI

Job Pool

Render

AI AI AI ...

Render

Physics Physics

AI AI AI AI ...

AI AI Physics

AI Physics AI

AI AI AI AI AI

Worker Threads

Tasks get subdivided

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Render

•N worker threads, 1 per processor core

•Sub-tasks spread out as needed

AI System

Graphics System

Physics System

Physics Physics

AI

Job Pool

Render

AI AI AI ...

Render

Physics Physics

AI AI AI AI ...

AI AI Physics

AI Physics AI

AI AI AI AI AI

Worker Threads

Tasks post changes

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Render

Post changes

Messaging

(change control)

AI System

Graphics System

Physics System

Physics Physics

AI

Job Pool

Render

AI AI AI ...

Render

Physics Physics

AI AI AI AI ...

AI AI Physics

AI Physics AI

AI AI AI AI AI

Worker Threads

Each thread has queued changes

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Render

Messaging

(change control)

C1

C2

C3

C4

C5

C6C7

AI System

Graphics System

Physics System

Physics Physics

AI

Job Pool

Render

AI AI AI ...

Render

Physics Physics

AI AI AI AI ...

AI AI Physics

AI Physics AI

AI AI AI AI AI

Worker Threads

Changes are sent to observers

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Render

C1

C2

C3

C4

C5

C6C7

Change Occurred

Messaging

(change control)

Good news/bad news: systems can (must) chunk up work•Some systems are very good at this (physics, fire, volumetric smoke, animation)

•Harder in other cases (graphics, script)

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Sounds great, what makes this harder?•Messaging system isn’t natural for sharing some data

•Service manager selectively exposes framework/system interfaces

•How do collision and AI work without data from multiple systems?

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Graphics and animation show it all

•Using Ogre3D•Extending window

– Display performance stats– Debug output

•Extending Ogre’s animation– Drive skeletal based data to provide realistic creature

expressions and locomotion– Use skeletons and weight maps– Hierarchical skeletal animation supports animation

blending

17Orion Granatir

Scene layout is configurable

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Meteor.Object FireBall.Object

Physics

Properties

FallingMeteorOnFire.Object

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How do we put a scene together?

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<Scene><Include CDF="House.Scene"/><Include CDF="Sky.Object"/><Include CDF="Terrain.Object"/>

// Meteor 1<Include ODF="FallingMeteorOnFire.Object"/>// Meteor 2<Include ODF="FallingMeteorOnFire.Object"/>...// Meteor 10<Include ODF="FallingMeteorOnFire.Object"/>

</Scene>

SmokeDemo.Scene

The fire system burns brightly!•Propagates naturally

•Smart particle systems use heat particles from each fire to spread procedurally

•Configurable density, velocity, direction, etc.

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Procedural trees•Editable grammar

and seeded parser– Easy to create an

endless variety of trees

•Canopies can be added, changed, or removed for seasonal effects

•Create Forests: each seed creates a different tree

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Physics rocks (and shatters)!

• Integrated physics– ODE/Newton– Havok (with

CharacterProxy and BreakOffParts)

– Bullet Physics Library

•Porting all systems to work with different physics

•Physics issues jobs that we put in thread pool as tasks

AI makes the world appear alive

•Flocks of chickens, herds of horses, and swoops of swallows all interact with the scene using custom AIs

•“Smart” enough to find companions, fear fire, and avoid falling objects

•AI was built from the ground up to be highly threaded

•AI drives velocity changes, uses Havok’s Character Proxy to interact w/environment

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Sometimes, things go wrong

Heavy contention on global sync object Per-thread sync

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What’s next for Smoke?

•Continuing development

•Look for public showing later in 2008

•Code and white paper release to follow

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Lessons learned (so far)Do:•Evaluate the features of your middleware for integration.•Find the best “chunking” in your systems.•Measure, understand and tune your performance/content.•Be the one that figures this all out!

Don’t:

• Ignore thread interaction between systems, especially middleware.

•Panic. No one method works for everybody.•Forget to share your great success stories at GDC 2009!

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Questions from the attendees

•What do you think?

•Where should we go from here? Any favorite technologies we should integrate?

•Have you tried something like this? How did it go?

•Have you rejected trying something like this? Why?

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