Performance is an important feature for many projects. Unfortunately, it's an all too common situation when a developer accidentally spoils the performance adding some new code. After a series of such incidents, people often start to think about performance regression testing.
As developers, we write unit tests all the time. These tests check that our business logic work as designed and that new features don't break existing code. It looks like a good idea to write some perf tests as well, which will verify that we don't have any performance regressions.
Turns out this is harder than it sounds. A lot of developers don't write perf tests at all. Some teams write perf tests, but almost all of them use their own infrastructure for analysis (which is not a bad thing in general because it's usually designed for specific projects and requirements). There are a lot of books about test-driven development (TDD), but there are no books about performance-driven development (PDD). There are well-known libraries for unit-testing (like xUnit/NUnit/MSTest for .NET), but there are almost no libraries for performance regression testing. Yeah, of course, there are some libraries which you can use. But there are troubles with well-known all recognized libraries, approaches, and tools. Ask your colleagues about it: some of them will give you different answers, the rest of them will start Googling it.
There is no common understanding of what performance testing should look like. This situation exists because it's really hard to develop a solution which solves all problems for all kind of projects. However, it doesn't mean that we shouldn't try. And we should try, we should share our experience and discuss best practices.Read more Comments
A few days ago Stephen Toub published a great post at the Microsoft .NET Blog: Performance Improvements in .NET Core. He showed some significant performance changes in .NET Core 2.0 Preview 1 (compared with .NET Framework 4.7). The .NET Core uses RyuJIT for generating assembly code. When I first tried RyuJIT (e.g., CTP2, CTP5, 2014), I wasn't excited about this: the preview versions had some bugs, and it worked slowly on my applications. However, the idea of a rethought and open-source JIT-compiler was a huge step forward and investment in the future. RyuJIT had been developed very actively in recent years: not only by Microsoft but with the help of the community. I'm still not happy about the generated assembly code in some methods, but I have to admit that the RyuJIT (as a part of .NET Core) works pretty well today: it shows a good performance level not only on artificial benchmarks but also on real user code. Also, there are a lot of changes not only in dotnet/coreclr (the .NET Core runtime), but also in dotnet/corefx (the .NET Core foundational libraries). It's very nice to watch how the community helps to optimize well-used classes which have not changed for years.
Now let's talk about benchmarks. For the demonstration, Stephen wrote a set of handwritten benchmarks. A few people (in comments and on HackerNews) asked about BenchmarkDotNet regarding these samples (as a better tool for performance measurements). So, I decided to try all these benchmarks on BenchmarkDotNet.
In this post, we will discuss how can BenchmarkDotNet help in such performance investigations, which benchmarking approaches (and when) are better to use, and how can we improve these measurements.Read more Comments