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Title:

THQ/Gas Powered Games Supreme Commander and Supreme Commander: Forged Alliance

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Title: GDC tutorial - GPG Supreme Commander threading case study Author: Intel Last modified by: Bradley J. Werth Created Date: 1/3/2006 3:33:43 AM – PowerPoint PPT presentation

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Title: THQ/Gas Powered Games Supreme Commander and Supreme Commander: Forged Alliance


1
THQ/Gas Powered GamesSupreme CommanderandSuprem
e CommanderForged Alliance
  • Thread for Performance

2
Supreme Commander runsbest on 4 cores - lets
see how!
  • Threading in mid-project can be done!
  • Decoupled threads give great performance
  • Memory management extends the gains
  • Lessons learned

3
Threading was a mid-stream change
  • Code was initially single-threaded
  • Game demanded more performance
  • Changed mid-project (6-12 months into
    development)
  • Separate render/sim threads to run at different
    rates
  • Support multiple cores
  • Limited architecture choices due to existing code
  • Using Boost thread library
  • Portable, open-source thread library

4
Render split is essential to speed
  • Lots of little threads sound, loading, etc.
  • Sim thread All simulation
  • Render thread Full speed, lt10x per sim tick
  • Sync phase Once frame is ready to render
  • Sync render and sim
  • Fully queued in and out of sim
  • Fast

5
Decoupled architecture is built for speed
Issue
  • Ready to start a frame and a simulation tick

6
Decoupled architecture is built for speed
Issue
Simulation
Sim Thread Interface
Render
Run decoupled sim and render Fully buffered input
to sim, call via Sim Thread Interface
7
Decoupled architecture is built for speed
Issue
  • Render can run repeatedly
  • Depends on sim duration

Simulation
Render
Render

Up to 10x per sim tick
8
Decoupled architecture is built for speed
  • Fully decoupled? No.
  • A few low level systems have locks.
  • No major performance impact!

Issue
Simulation
Locks
Render
Render

Up to 10x per sim tick
9
Decoupled architecture is built for speed
Issue
Issue
Simulation
Sim Thread Interface
Render
Render
Render
  • Sync sim thread out to render thread,
  • via STI again


Up to 10x per sim tick
10
Decoupled architecture is built for speed
Issue
Issue
Simulation
Sim Thread Interface
Sim Thread Interface
  • Multiplayer Record everything going through STI
  • Send over network

Render
Render
Render

Up to 10x per sim tick
11
Decoupled architecture is built for speed
Issue
Issue
Issue
Simulation
Sim
Render
Render
Render
Render

  • And so on

Up to 10x per sim tick
12
Thread model adapts to varying loads
  • Architecture scales well with loads
  • Render load will often dominate
  • Re-render to keep frame rates up
  • Sim-heavy map will try to be sim-dominated

13
Displaying frame times cool!
  • Thread stats in real time

14
Sometimes, theres more to render
  • Render
  • Runs as fast as possible
  • Simulation
  • Sim/render sync
  • Both threads synced, fully queued in and out of
    sim

15
Other times, theres more to simulate
  • Sim runs across many rendered frames

16
A little sync doesnt slow this code down
Threads are busy most of the time!
Frame n
Frame n1
Sync
Waiting
Busy
Mostly waiting
17
Memory manager gives an additional boost
  • Memory If youre not careful in a threaded game
  • Memory use can thrash cache but not a problem
    here!
  • Memory alloc/free can be slow
  • Suspected memory management was problem
  • Doing lots of small allocations
  • Built code to make it easy to switch mem managers
  • Custom mem manager outperforms default
    malloc/free
  • Can cause some debugging questions
  • Purchased commercial one for Supreme Commander
  • Wrote new one for Forged Alliance

18
What are some current bottlenecks?
  • Multiplayer all sims run concurrently
  • Limited by least-common-denominator machine
  • Thats the RTS way
  • Monolithic render thread
  • Multiple monitors, typically different views
  • Possibly split off top part of render for second
    monitor?
  • Too expensive/complex for niche feature

19
This was a great learning experience!
  • Good intermediate step
  • Especially for threading mid-project
  • Would do it differently if doing it from scratch
  • Target more processor cores
  • General worker threads w/dispatch system
  • Templates to define an interface to common
    semantics
  • Directed work graph/node graph (hard to express)
  • Or ?
  • The engine is so good, itll be back in Demigod!
  • Demigod team using modified Supreme Commander
    engine

20
We learned some DOs and DONTs
  • Do
  • Architect for threading from the start, if you
    can
  • Thread single-threaded code, if you must
  • Decouple threads where possible
  • Dont
  • Be afraid to thread single-threaded code

21
Supreme Commander runsbest on 4 cores thats
how!
  • Threading in mid-project can be done!
  • Decoupled threads give great performance
  • Memory management extends the gains
  • Lessons learned

22
So, what do you think?
  • Have you tried something like this?
  • Successes?
  • Failures?
  • Have you rejected trying something like this?
  • Why?

23
(No Transcript)
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