parallelizing a real-time steering simulation for computer games with openmp by bjoern knafla and...

Parallelizinga Real-Time

Steering Simulation for Computer Games

withOpenMP

Bjoern Knafla and Claudia LeopoldUniversity of Kassel (Germany)

1Dienstag, 11. September 2007

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Steering a flock of birds

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Bird

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BirdBoid

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BirdBoid

Agent

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CPU

core

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CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

CPU

core

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4Dienstag, 11. September 2007

Outline

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Outline

1. Steering behaviors

5Dienstag, 11. September 2007

Outline

1. Steering behaviors

2. OpenSteerDemo

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Outline

1. Steering behaviors

2. OpenSteerDemo

3. Bad parallelization

5Dienstag, 11. September 2007

Outline

1. Steering behaviors

2. OpenSteerDemo

3. Bad parallelization

4. Parallelization that works

5Dienstag, 11. September 2007

Outline

1. Steering behaviors

2. OpenSteerDemo

3. Bad parallelization

4. Parallelization that works

5. Performance

5Dienstag, 11. September 2007

Outline

1. Steering behaviors

2. OpenSteerDemo

3. Bad parallelization

4. Parallelization that works

5. Performance

6. Summary

5Dienstag, 11. September 2007

Steering behaviors

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Alignment8Dienstag, 11. September 2007

OpenSteerDemo

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OpenSteerDemo

Testbed for the open source library OpenSteer from Craig W. Reynods

9Dienstag, 11. September 2007

OpenSteerDemo

Testbed for the open source library OpenSteer from Craig W. Reynods

Simulates steering behavior of agents

9Dienstag, 11. September 2007

OpenSteerDemo

Testbed for the open source library OpenSteer from Craig W. Reynods

Simulates steering behavior of agents

Game-like C++ real-time application

9Dienstag, 11. September 2007

OpenSteerDemo

Testbed for the open source library OpenSteer from Craig W. Reynods

Simulates steering behavior of agents

Game-like C++ real-time application

OpenGL

9Dienstag, 11. September 2007

OpenSteerDemo

Testbed for the open source library OpenSteer from Craig W. Reynods

Simulates steering behavior of agents

Game-like C++ real-time application

OpenGL

http://opensteer.sourceforge.net

9Dienstag, 11. September 2007

Main loop

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Main loop

Input Update Output

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Input Update Graph-

ics

Main loop

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Input stage

Time step t

Input Update Graph-

ics

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Update stage

Time step t

Input Update Graph-

ics

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Graphics stage

Time step t

Input Update Graph-

ics

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Next main loop cycle

Time step t+1

Input Update Graph-

ics

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Update stage

Input Update Graph-

ics

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Agent update

Update

agent

Neighbors Random.Agent

state

read + write read + write read + write

references

Graphics

write

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Time step t

Sequentialagent

updateorder

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...

In state t-1

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Time step t

Sequentialagent

updateorder

Neighbors

In state t-1

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...

In state t-1

18Dienstag, 11. September 2007

Time step t

Sequentialagent

updateorder

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...

In state t-1

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Time step t

Sequentialagent

updateorder

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...

In state t-1In state t

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Time step t

Sequentialagent

updateorder

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...

In state t-1In state t

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Time step t

Sequentialagent

updateorder

Neighbors

In state ?

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...

In state t-1In state t

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Bad parallelization

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Questionable reliabilityand correctness

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No speedup

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No speedup

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Mainparallelization problems

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Race conditions

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Race conditions

Global variables, deep inheritance hierarchies, strongly interdependent classes

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Race conditions

Global variables, deep inheritance hierarchies, strongly interdependent classes

Non-determinism

26Dienstag, 11. September 2007

Race conditions

Global variables, deep inheritance hierarchies, strongly interdependent classes

Non-determinism

Order of agent updates and random numbers

26Dienstag, 11. September 2007

Race conditions

Global variables, deep inheritance hierarchies, strongly interdependent classes

Non-determinism

Order of agent updates and random numbers

Non-thread-safe functions

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Parallelizationthat works

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Guiding ideas

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Guiding ideas

Update order independent simulation

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Guiding ideas

Update order independent simulation

Agent modification only dependent on its steering vector

28Dienstag, 11. September 2007

Guiding ideas

Update order independent simulation

Agent modification only dependent on its steering vector

Minimize synchronization

28Dienstag, 11. September 2007

Guiding ideas

Update order independent simulation

Agent modification only dependent on its steering vector

Minimize synchronization

Finish parallel processing before graphics stage

28Dienstag, 11. September 2007

Guiding ideas

Update order independent simulation

Agent modification only dependent on its steering vector

Minimize synchronization

Finish parallel processing before graphics stage

Interfaces for explicit context

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Refactorization

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Split agent update

Agentupdateorder

Sim.

agent

Modify

agent

Agent update

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Simulate agent stage

Agent public

Agent private

Sim.

agent

Random.

Agent

state

Agent

stateNeighbors

Render-

Feeder

references

readread

read + write

write

Steering

Vector

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Simulate agent stage

Agent public

Agent private

Sim.

agent

Random.

Agent

state

Agent

stateNeighbors

Render-

Feeder

references

readread

read + write

write

Steering

Vectorconst

const

31Dienstag, 11. September 2007

Modify agent stage

Agent public

Agent private

Modify

agent

Random.

Agent

state

Agent

stateNeighbors

Render-

Feeder

references

read + write

read

Steering

Vector

32Dienstag, 11. September 2007

Modify neighbor data structure

Agent public

Agent private

Modify

neigh-

bors

Random.

Agent

state

Agent

stateNeighbors

Render-

Feeder

references

write

Steering

Vector read

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Input Update Output

Refactor update stage

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Split update stage

Sub-stages: simulation and modification

Sim. Modify

Update stage

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Old update stage

Sequentialprocessing

order

Sim.

agent

0

Modify

agent

0

Sim.

agent

1

Modify

agent

1

Sim.

agent

n

Modify

agent

n

...

Update agent Update agent Update agent

36Dienstag, 11. September 2007

Time step t

Sequentialprocessing

order

Sim.

agent

0

Modify

agent

0

Sim.

agent

1

Modify

agent

1

Sim.

agent

n

Modify

agent

n

...

Agents in state t-1

37Dienstag, 11. September 2007

Time step t

Sequentialprocessing

order

Sim.

agent

0

Modify

agent

0

Sim.

agent

1

Modify

agent

1

Sim.

agent

n

Modify

agent

n

...

Agent in state t Agents in state t-1

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New update stage

Sequentialprocessing

order

Sim.

agent

0

Sim.

agent

1

...

Sim.

agent

n

Modify

agent

0

Modify

agent

1

...

Modify

agent

n

Simulation sub-stage Modification sub-stage

39Dienstag, 11. September 2007

Time step t

Sequentialprocessing

order

Sim.

agent

0

Sim.

agent

1

...

Sim.

agent

n

Modify

agent

0

Modify

agent

1

...

Modify

agent

n

Agents in public state t-1

40Dienstag, 11. September 2007

Time step t

Sequentialprocessing

order

Sim.

agent

0

Sim.

agent

1

...

Sim.

agent

n

Modify

agent

0

Modify

agent

1

...

Modify

agent

n

Agents in public state t-1

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Time step t

Sequentialprocessing

order

Sim.

agent

0

Sim.

agent

1

...

Sim.

agent

n

Modify

agent

0

Modify

agent

1

...

Modify

agent

n

Agents in public state t-1

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Time step t

Each agent is modifiedbased solely on its ownstate

Sequentialprocessing

order

Sim.

agent

0

Sim.

agent

1

...

Sim.

agent

n

Modify

agent

0

Modify

agent

1

...

Modify

agent

n

Agents in public state t-1

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Parallelization

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Parallel update stage

S M

B

a

r

r

i

e

r

P

a

r

a

l

l

e

l

Simulation

B

a

r

r

i

e

r

P

a

r

a

l

l

e

l

Modification

Update

neigh-

bors

Possibly

parallelS S

S S

S S S

S S

SS

M M

M M M

M M M

M M M

M M M

44Dienstag, 11. September 2007

Parallel simulationsub-stage

S

B

a

r

r

i

e

r

P

a

r

a

l

l

e

l

Simulation

B

a

r

r

i

e

r

P

a

r

a

l

l

e

l

Modification

Update

neigh-

bors

Possibly

parallelS S

S S

S S S

S S

SS

45Dienstag, 11. September 2007

Parallel modificationsub-stage

M

B

a

r

r

i

e

r

P

a

r

a

l

l

e

l

Simulation

B

a

r

r

i

e

r

P

a

r

a

l

l

e

l

Modification

Update

neigh-

bors

Possibly

parallelM M

M M M

M M M

M M M

M M M

46Dienstag, 11. September 2007

Parallel modificationsub-stage

B

a

r

r

i

e

r

P

a

r

a

l

l

e

l

Simulation

B

a

r

r

i

e

r

P

a

r

a

l

l

e

l

Modification

Update

neigh-

bors

Possibly

parallel

47Dienstag, 11. September 2007

Performance

48Dienstag, 11. September 2007

Dual-processor dual-core 2 GHz AMD Opteron with 2 GB Ram

2x Nvidia 7800 GTX graphics cards in SLI mode

Linux OS

Test-computer

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Max speedups

50Dienstag, 11. September 2007

Comparison of OpenSteerDemo flock of birds simulation with 4 threads with OpenMP-disabled version

Max speedups

50Dienstag, 11. September 2007

Comparison of OpenSteerDemo flock of birds simulation with 4 threads with OpenMP-disabled version

Whole application: !2.84

Max speedups

50Dienstag, 11. September 2007

Comparison of OpenSteerDemo flock of birds simulation with 4 threads with OpenMP-disabled version

Whole application: !2.84

Update stage: !! ! 3.54

Max speedups

50Dienstag, 11. September 2007

Summary

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52Dienstag, 11. September 2007

Refactored first

52Dienstag, 11. September 2007

Refactored first

Simplicity!

52Dienstag, 11. September 2007

Refactored first

Simplicity!

High-level design to min. synchronization

52Dienstag, 11. September 2007

Refactored first

Simplicity!

High-level design to min. synchronization

Explicit context

52Dienstag, 11. September 2007

Refactored first

Simplicity!

High-level design to min. synchronization

Explicit context

Deferred computation

52Dienstag, 11. September 2007

Refactored first

Simplicity!

High-level design to min. synchronization

Explicit context

Deferred computation

Identified slices for data-parallel computation

52Dienstag, 11. September 2007

Thank you!

53Dienstag, 11. September 2007