[In this Sponsored Feature, part of Intel's Visual Computing microsite, Shrout and Davies examine the 'shift in processor architecture and design over the last few years' that has changed once simple rules regarding CPUs and computer chips in general into a 'much more complicated scenario'.]

Introduction

No matter what platform you work on, developing a game can be a lot like trying to build something on quicksand: Somewhere between the time you start designing the game and the day it launches, the landscape you thought you were developing for shifts.

This might be a simple change to the game design, the inclusion of a new graphic technique to a more drastic shift to a completely new hardware platform, while on the PC the hardware installed based is constantly evolving. That is, while you were busy writing game code for the current hardware in the studio, the hardware industry has been aggressively increasing processor performance and adding new features to your customers' PCs.

Until as recently as 2005 the main processor advances were targeted at improving single threaded performance with each generation offering higher operating frequencies and better instruction level parallelism. Developers assumed that as newer processors were released they would "just be faster," and the code and applications would scale accordingly, frequently code was designed with the assumption the top end PC at the time of release would be faster than the development system the original code was written on.

However, a shift in processor architecture and design over the last few years has changed this one-time rule into a much more complicated scenario. With the introduction of the Intel Core i7 processor game developers can now up to eight times the number of computing threads that were once available.

Processor speed and features are no longer increasing in simply a linear fashion and new technologies such as turbo boost can have a significant impact on the system's performance, making it critical that the code written for any application be able to not only scale from processor generation to generation but also reliably adapt to future architectures down the road.

Innovation on a Timeline

This fundamental shift in processor performance is a result of the many technical innovations in the world of processor architecture. Even in the last three years we have seen at least two cycles of the Intel "tick-tock" model of improvements: The "tick" introduces a die shrink process technology

that allows designers to fit more transistors in the same physical die space, while the "tock" introduces a new microarchitecture with performance and feature enhancements.

During the "tick" years the process technology has evolved from 65nm-generation products introduced in 2005 to 45nm generation in 2007 and will become 32nm by the end of 2009. During the "tock" years the original Intel Pentium processor microarchitecture evolved into the Intel Core microarchitecture in 2006, leading to the introduction of the Intel Core i7 processor and a new microarchitecture in 2008. Figure 1 illustrates this progression.

Figure 1. Intel's "tick-tock" model of architecture progression.

The upcoming Sandy Bridge microarchitecture will be introduced in 2010 and, in keeping with the other architectures shown in Figure 1, will differ dramatically from previous-generation processors. Although code written and optimized for one architecture will run on succeeding architectures, developers can frequently improve performance going forward and avoid potential performance pitfalls as new processors are released by ensuring their code can enumerate the hardware it's running on and adapt to it.

Programming with Multiple-Threads in Mind

For many years the hardware and software development cycles were mostly independent of each other. Programmers of compilers and other low-level applications needed intricate knowledge of the hardware underneath in order to extract the best performance from the platform, while games relied on the compiler to optimize the game code for the hardware while the coder concentrated on finding the best algorithm for the job . Today the same level of hardware expertise is now required for more general computing tasks, such as game development. And it's easy to understand why.

Average game development takes from about one to three years, and any new core engine technology must be programmed to last even longer on the market as it will likely span multiple shipping titles; it is not unusual for a large-scale game engine to take up to five years total development time from inception to shipping. Intel's rapid-development tick-tock model means the average game engine will need to span many different processor architectures.

The introduction of multi-core processors (rather than simply higher clocked processors) means that developers need to write code that scales to make use of that hardware. With the increasing emphasis on improving processor power through larger core counts, the hardware can no longer speed up existing code easily unless the designer has purposely built the software with multi-threading in mind. Consider the Intel Core i7 processor in Figure 2, to fully utilize this processor the game would need to use 8 threads communicating through a hierarchical cache.

Programming decisions made today will dramatically impact, the performance of a game on future architectures. So although processors are continually getting faster and more powerful, developers must make sure they are properly using the computing power at their disposal.