Performance evaluation for most software products is a very scientific process. First, we determine the maximum/minimum supported performance metrics, such as the allowed memory usage, acceptable CPU consumption, the number of concurrent users, and so on. Next, we perform load testing against the application in scenarios with a version of the application built for the target platform, and test it while gathering instrumentation data. Once this data is collected, we analyze and search it for performance bottlenecks. If problems are discovered, we complete a root-cause analysis, make changes in the configuration or application code to fix the issue and repeat it.
Although game development is a very artistic process, it is still exceptionally technical, so there is a good reason to treat it in similarly objective ways. Our game should have a target audience in mind, which can tell us what hardware limitations our game might be operating under and, perhaps, tell us exactly what performance targets we need to meet (particularly in the case of console and mobile games). We can perform runtime testing on our application, gather performance data from multiple subsystems (CPU, GPU, memory, the Physics Engine, the Rendering Pipeline, and so on), and compare them against what we consider to be acceptable. We can use this data to identify bottlenecks in our application, perform additional instrumentation, and determine the root cause of the issue. Finally, depending on the type of problem, we should be capable of applying a number of fixes to improve our application's performance to bring it more in line with the intended behavior.
However, before we spend even a single moment making performance fixes, we will need to prove that a performance problem exists to begin with. It is unwise to spend time rewriting and refactoring code until there is good reason to do so, since pre-optimization is rarely worth the hassle. Once we have proof of a performance issue, the next task is figuring out exactly where the bottleneck is located. It is important to ensure that we understand why the performance issue is happening, otherwise we could waste even more time applying fixes that are little more than educated guesses. Doing so often means that we only fix a symptom of the issue, not its root cause, and so we risk the chance that it manifests itself in other ways in the future, or in ways we haven't yet detected.
In this chapter, we will explore the following:
- How to gather profiling data using the Unity Profiler
- How to analyze Profiler data for performance bottlenecks
- Techniques to isolate a performance problem and determine its root cause
With a thorough understanding of a given problem, you will then be ready for information presented in the remaining chapters, where you will learn what solutions are available for the issue we've detected.
