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

Steering a flock of birds


Bird


BirdBoid


BirdBoid

Agent


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

CPU

core


Outline


Outline

1. Steering behaviors


Outline


2. OpenSteerDemo


Outline


2. OpenSteerDemo

3. Bad parallelization


Outline


2. OpenSteerDemo


4. Parallelization that works


Outline


2. OpenSteerDemo



5. Performance


Outline


2. OpenSteerDemo



5. Performance

6. Summary


Steering behaviors


Alignment8Dienstag, 11. September 2007

OpenSteerDemo


OpenSteerDemo

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


OpenSteerDemo


Simulates steering behavior of agents


OpenSteerDemo



Game-like C++ real-time application


OpenSteerDemo




OpenGL


OpenSteerDemo




OpenGL

http://opensteer.sourceforge.net




Main loop


Main loop

Input Update Output


Input Update Graph-

ics

Main loop


Input stage

Time step t

Input Update Graph-

ics


Update stage

Time step t

Input Update Graph-

ics


Graphics stage

Time step t

Input Update Graph-

ics


Next main loop cycle

Time step t+1

Input Update Graph-

ics


Update stage

Input Update Graph-

ics


Agent update

Update

agent

Neighbors Random.Agent

state

read + write read + write read + write

references

Graphics

write


Time step t

Sequentialagent

updateorder

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...

In state t-1


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


Time step t

Sequentialagent

updateorder

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...

In state t-1


Time step t

Sequentialagent

updateorder

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...

In state t-1In state t


Time step t

Sequentialagent

updateorder

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...



Time step t

Sequentialagent

updateorder

Neighbors

In state ?

Update

agent

0

Update

agent

1

Update

agent

2

Update

agent

n

...



Bad parallelization


Questionable reliabilityand correctness


No speedup


Mainparallelization problems


Race conditions


Race conditions

Global variables, deep inheritance hierarchies, strongly interdependent classes


Race conditions


Non-determinism


Race conditions


Non-determinism

Order of agent updates and random numbers


Race conditions


Non-determinism

Order of agent updates and random numbers

Non-thread-safe functions


Parallelizationthat works


Guiding ideas


Guiding ideas

Update order independent simulation


Guiding ideas


Agent modification only dependent on its steering vector


Guiding ideas



Minimize synchronization


Guiding ideas




Finish parallel processing before graphics stage


Guiding ideas




Finish parallel processing before graphics stage

Interfaces for explicit context


Refactorization


Split agent update

Agentupdateorder

Sim.

agent

Modify

agent

Agent update


Simulate agent stage

Agent public

Agent private

Sim.

agent

Random.

Agent

state

Agent

stateNeighbors

Render-

Feeder

references

readread

read + write

write

Steering

Vector


Simulate agent stage

Agent public

Agent private

Sim.

agent

Random.

Agent

state

Agent

stateNeighbors

Render-

Feeder

references

readread

read + write

write

Steering

Vectorconst

const


Modify agent stage

Agent public

Agent private

Modify

agent

Random.

Agent

state

Agent

stateNeighbors

Render-

Feeder

references

read + write

read

Steering

Vector


Modify neighbor data structure

Agent public

Agent private

Modify

neigh-

bors

Random.

Agent

state

Agent

stateNeighbors

Render-

Feeder

references

write

Steering

Vector read


Input Update Output

Refactor update stage


Split update stage

Sub-stages: simulation and modification

Sim. Modify

Update stage


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


Time step t


order

Sim.

agent

0

Modify

agent

0

Sim.

agent

1

Modify

agent

1

Sim.

agent

n

Modify

agent

n

...

Agents in state t-1


Time step t


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


New update stage


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


Time step t


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


Time step t


order

Sim.

agent

0

Sim.

agent

1

...

Sim.

agent

n

Modify

agent

0

Modify

agent

1

...

Modify

agent

n



Time step t

Each agent is modifiedbased solely on its ownstate


order

Sim.

agent

0

Sim.

agent

1

...

Sim.

agent

n

Modify

agent

0

Modify

agent

1

...

Modify

agent

n



Parallelization


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


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


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


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


Performance


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


Max speedups


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

Max speedups



Whole application: !2.84

Max speedups



Whole application: !2.84

Update stage: !! ! 3.54

Max speedups


Summary


Refactored first


Refactored first

Simplicity!


Refactored first

Simplicity!

High-level design to min. synchronization


Refactored first

Simplicity!


Explicit context


Refactored first

Simplicity!


Explicit context

Deferred computation


Refactored first

Simplicity!


Explicit context

Deferred computation

Identified slices for data-parallel computation


Thank you!


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

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