Allegorithmic Substance Threaded Middleware. 2 Procedural textures on multi-core Other than...

AllegorithmicSubstance

Threaded Middleware

2

Procedural textures on multi-core

•Other than framerate and features, what else can you do with extra CPU power ?

•We’ll look at Allegorithmic’s middleware, Substance

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Procedural textures are valuable for modern games

•Have a LOT of textures.•Want shorter loading times ( , faster starts

)teleportations or zooms .•Need to reduce texture memory on a disc, for

download, and/or in RAM.•Can benefit from more flexible and reusable

assets.

Introducing Substance

In Q2 2007 Allegorithmic started a complete reengineering of ProFX2, authoring tool and engine, named Substance.

Unit tests were done very early to ensure that Substance could target streaming.

Cross-platform : PC, PS3, XBOX, etc. Expected linear multi-thread scalability.

What is Substance ?

Substance is a middleware product composed of two elements.

Substance Authoring Tool lets you create procedural textures create texture packages of a few kilobytes ! A cooker compiles generic data into binaries

optimized for a specific platform or user. Substance Engine

generates bitmap textures on the fly.

Less FPS ?

More textures, not less FPS Substance consumes idle cycles, not frames

Graphics bitrates follow Moore's law Higher poly count → bigger worlds Higher filter rate → larger textures Desired texture volume grows faster than RAM

Streaming is a necessity But HDD net bitrate does not follow. Bottleneck !

Modern gameplay entails sudden bitrate bursts This is worsened by HDD seeks and entails stalls.

No, a stable and high FPS.

Even masked, a stall is actually a FPS drop Substance works in Random Access Memory The gamer zooms or teleports:

Give 4 cores and a GPU to Substance Sacrifice 1 or 2 frames Substance gen. & cache 1-2M new texels. The stall does not hinder game play.

Substance diminishes stalls Substance helps to maintain a high FPS.

Performance issue:streaming in games

DVD or HDD net bitrate is 2 or 6 MB/s Our aim: add a stable 4MB/s without the GPU Requires billions of intermediate pixels/s. Can CPUs compete with GPUs ? Opportunity: cores are still under-exploited in

most game engines. Texture processing is privileged in the new

multi-core architectures.

The architecture was designed with these issues in mind:

Homogeneous CPU and GPU versions Streaming (~1-10 CPU cycles per pixel) SIMD & MT for the multi-core generations No cache nor threading pollution Fine grained jobs and lockless sync. Low memory footprint

The theoretical benefit was calculated

New architectures come with enhanced SIMD. Expected x10 compared to std C++

Tricks and algorithmic changes could give another x10 on some filters, like DXT

We were confident that our image processes could be well threaded. Partly because we generate textures asynchronously

Hence the CPU version of ProFX2 could be accelerated by a factor x25-x100

This is the approach taken to address the issue:

Simple innerloop tests actually showed that optimized SSE2-4 code could give a boost of x10

Find a data layout coherent with micro parallelism (SIMD and pipeline), low level threading, cache and memory handling.

OpenMP is then used to test strategies before designing a specific MT HAL

Here’s the code that was developed to make this possible:

A SIMD HAL is ready for PC, Xbox, PS3. OpenMP easily gives a 85% MT linearity. Our MT HAL is converging towards a model of

lockless synchronization, 95% expected. The cooker precomputes data that will help

synchronization and MT efficiency. Our API exposes asynchronous commands.

Perfect to share cores with a game loop !

The compositing graph,node based image processing

Authoring Tool: non linear editing Engine: efficient high level structure Graph (DAG) contains 3 types of nodes:

Sources: procedural noise, bitmaps, SVGs Filters: blend, HSL, TRS, warp, blur, etc. Outputs: coherent diffuse & normal maps, etc.

Main advantages: Libraries, capsules: instanciation of subgraphs Complex variants: fast to create and compute Dynamic custom branches (ex: aging textures)

The compositing graph,node based image processing

Threading strategies

High level threading: Task decomposition : 1 node (filter) per thread Graph splitting ensures task independency

Low level threading: Data decomposition : 1 strip of blocks per thread Dispatcher ensures non conflicting areas Pixel to pixel filters are concatenated. Streamed R/W, no L2 cache pollution Temporary blocks in private L1 double buffers Intermediate images never allocated Lockless reactive sync and cache friendly

Threading sub graphs (1/11)by nodes (high level)

Threading sub graphs (2/11)by nodes, caching

Threading sub graphs (3/11)by nodes

Threading sub graphs (4/11)by strips (low level)

Threading sub graphs (5/11)remove from cache

Threading sub graphs (6/11)by strips

Threading sub graphs (7/11)remove from cache

Threading sub graphs (8/11)by strips

Threading sub graphs (9/11)remove from cache

Threading sub graphs (10/11)by strips

Threading sub graphs (11/11)update cache, and finished

Expect more streaming bandwidth

Substance generates 4MB/s of compressed textures per second

Cumulate this with classical streaming 50+ MB/s loading with 4 cores and 1 GPU

streaming1/2 core

1 core2 cores

2 cores4 cores

4 coresadd GPU

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50 GPUPenrynYorkfieldCD, DVD

Here’s how close we got to the theoretical best performance:

DXT compression at 2G pixels/s (same as what hi-end GPUs can do in 2007).

8 bits SVG (cooked) rendering at 20G/s. 8G/s anti-aliasing with 4 sub-samples.

In most cases 4 cores give a x3.8 boost Some filters are more problematic, but solutions

have been imagined in details, and will be implemented between Q2 and Q4 2008.

Here’s the new performance profile:

DXT TRS Blend SVG0

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ProFX2Substance

Substance and ProFX2 figures are for one core.

4 cores: 3.8 times more fillrate.

ProFX2: SVG GPU Substance: SVG CPU SVG AA: 2G pixels/s

per core

This is future-proofed

The cooker precomputes whatever helps to linearise computations.

Scalable code: SSE4 added in one day thanks to the SIMD HAL

Scalable threading: our two strategies scale A few functions dispatch virtual CPU "shaders" 64-cores ready ↔ code a new dispatcher ? Multiplatform design.

What’s next?

Procedural diffuse map

Coherent procedural normal map

Complex procedural environment map

This scene is made entirely of

proceduraltextures

Future sources of bandwidth

SIMD code can be better pipelined in ASM. Our cooker can optimize a lot of things. Authoring tool will have a RT profiler Artists gaining experience with Substance will

also optimize their packages better. Artist feedback will also help us to improve the

expressiveness of each filter ~30-50 filters per texture, main perf. divisor.

Here’s how you can best take advantage of procedural textures

Anticipate texture generation requests. Predict visibility (HOM, PVS). Create mipmaps. Access levels JIT. Cache the useful texels. Adapt texture resolution to workload. Use texture variants, less tiling textures or

details. Show a higher texel/pixel ratio.

What do you think?

Have you tried something like this? Have you rejected trying something like this?