Dragged, Kicking and Screaming: Multicore Architecture and Video Games

Summary of Topics: Console Architecture Meaning of Paper’s Title/Why the Video Game Developer HATED the new Techniques/Problems The Future

Video Game Architecture For the most part, same as computer: Very operating system-linked. With PCs, almost always have been games. Mac Gaming is sparse, recently increased. Linux users have to compile/make their own. Console Games = primarily single-core processors…until 2005.

XBOX GHz “Xenon” triple-core PowerPC, 2 hardware threads per processor 256 MB main RAM 500 MHz ATI “Xenos” GPU -CPU accesses memory through the GPU! GPU has 10 MB RAM embedded frame buffer

XBOX 360 vs. Playstation 3 Triple-Core PPC Xbox MB, 700 MHz, GDDR3, shared by CPU and GPU CPU accesses memory through the GPU! GPU has 10 MB RAM embedded frame buffer Multicore Cell Engine PS MB total 256 MB 3.2 GHz XDR main RAM for the CPU 256 MB 700 MHz GDDR3 video RAM for the GPU

Multiple synergistic core units that attach to local stores, which then feed into DMAs going into the on-chip bus. One set-off PPE (Power Processing Element), with an L1 and L2 cache. Developers are having some serious problems with this model. Cell Architecture

Why So Unhappy? Delays, setbacks, ecetera = unhappy fans. Yu Suzuki; Saturn Virtua Fighter: “One very fast central processor would be preferable...I think that only one in 100 programmers are good enough to get this kind of speed out of the Saturn.” Not implementing parallelism, use of multicore architecture, etc = unhappy fans. If game developers utilize parallelism, the game will be delayed – 6 months, 1 year?

“I guess, if we have to.” Multicore Parallelism Implementations

Beginning Techniques Patches, so computers at least realize there’s multiple cores available. Patches, so computers at least realize there’s multiple cores available. Intel releases several multicore assists; especially in the beginning (coaxing people into it) Intel releases several multicore assists; especially in the beginning (coaxing people into it) Building Blocks Building Blocks Codeplay’s sieve compilers Codeplay’s sieve compilers Broke a program into “sieve blocks” where automatic parallelization could be utilized Broke a program into “sieve blocks” where automatic parallelization could be utilized

What do we do today? Multithreading from the ground up Decent (and fast!) parallelization One of two main ways: Every process on a different thread Dependencies galore~!

Main gaming thread, with branches coming off for specific parts of the game and splintering into other threads. Particularly beastly programs get their own multithreading implementations. Networking and I/O get their own threads. “Best” Multithreading Approach

CASE EXAMPLE: Kameo, which achieved 2.2~2.5 cores in 6mos. Rendering, decompression were on a separate thread Latter saved space on the DVD and improved load times for the game. Additionally, file I/O was separated onto two threads – one for reading, and one for decompressing. CASE EXAMPLE: Kameo

Best Processes for MT File decompression – improve load times. Rendering – separate update and render; can be problematic Physics Engine? – Physics/Update/Render, but latency issues. Graphical Fluff – always and forever. Artificial Intelligence - position independency of data, cache coherency

Cascade Project Fix dataflow by sending data from the parent to the child before the parent had completed! Respect dependencies, divided AI Resulted in reducing “the average time per frame from 15.5ms using a single thread to 7.8ms using eight threads.” 51% Speedup! Work in progress – CDML List constraints in language instead of working out later.

Multithreading is Tricky Threads can fight over the cache Dependencies Data corruption, deadlocks Bugs might not be apparent right away Debugging sets developers back

The Future ARM’s GPU/CPU Chip Intel’s Larrabee Chip Mobile Gaming Platforms laugh for now… Mobile Gaming Platforms laugh for now… Unreal 4 Engine – “We’re waiting for massively multicore processors.”

Thanks for watching! It’s just not that easy anymore.