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Performance Improvement of Ruby 2.7 JIT in Real World

Takashi Kokubun • May 22, 2019 • Minneapolis, MN

The video titled "Performance Improvement of Ruby 2.7 JIT in Real World" by Takashi Kokubun, presented at RailsConf 2019, focuses on the advancements in the Just-In-Time (JIT) compiler for Ruby 2.7, particularly how these improvements can enhance the performance of real-world applications, such as Ruby on Rails.

Key points discussed in the presentation include:

- Introduction to JIT Compiler: Takashi introduces the JIT compiler, explaining its role in optimizing Ruby code at runtime rather than at the time of compilation, which is a significant innovation for the Ruby language.

- Improvement from Ruby 2.6 to 2.7: Initial experiences with JIT in Ruby 2.6 showed limited performance gains for Rails applications, but the focus for 2.7 is on optimizing real-world application performance.

- Performance Benchmarks: The speaker presents several benchmarks showcasing JIT's performance improvements, including a notable comparison of JIT-enabled Ruby 2.6 which performed 1.6 times faster than non-JIT versions. However, these figures still show room for improvement, especially when compared to earlier versions like Ruby 2.0, where performance enhanced approximately 2.5 times.

- Real-world Applications Testing: A significant portion of the talk is dedicated to assessing the performance of Rails applications using the JIT compiler. A specific example highlighted is the use of the Discourse application as a benchmark to evaluate real-world performance.

- Challenges Encountered: Kokubun discusses various challenges faced while implementing the JIT compiler, such as overhead from calling dynamically generated code and memory management during performance optimization.

- Ongoing Improvements: The speaker describes ongoing efforts to address these performance issues, including stack allocation for objects and optimizing the method call overhead, which consumes a considerable amount of resources.

- Future Directions: Takashi concludes by indicating areas for further research and optimization in Ruby's performance, particularly emphasizing the need for detailed profiling and further improvements in JIT performance metrics.

By focusing on the JIT compiler's development and the practical implications for production Ruby applications, this talk highlights both current capabilities and future potential within the Ruby community, aiming for more efficient code execution in real-world scenarios.

Conclusions from the presentation emphasize that while significant improvements have been made, ongoing work is needed to further optimize Ruby's performance through enhancements in the JIT compiler, making it more effective for developers working in production environments.

Performance Improvement of Ruby 2.7 JIT in Real World
Takashi Kokubun • May 22, 2019 • Minneapolis, MN

RailsConf 2019 - Performance Improvement of Ruby 2.7 JIT in Real World by Takashi Kokubun

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Have you ever tried MRI's JIT compiler in Ruby 2.6? Unfortunately it had not improved Rails application performance while it achieved a good progress on some other benchmarks.

Beyond the progress at Ruby 2.6, JIT development on Ruby 2.7 will be dedicated to improve performance of real-world applications, especially Ruby on Rails. Come and join this talk to figure out how it's going well and what you should care about when you use it on production.

RailsConf 2019

00:00:20.660 Okay, so I started talking about the just-in-time compiler for Ruby. Since this is my first visit to RailsConf, let me introduce myself.
00:00:30.300 My name is Takashi Kokubun, and I am working at Rosetta. I've been a Ruby committer for about two to three years.
00:00:37.140 My main focus is on the Ruby on Rails application development. I began contributing as a Ruby maintainer and have been actively working on the JIT compiler.
00:00:46.379 This work is a side project for me, as my primary responsibility is within the business of Georgia Data.
00:00:54.680 After work, I spend my time working on the JIT compiler, so this talk is all about my side work on JIT.
00:01:07.050 JIT stands for just-in-time, and it is currently an experimental feature for Ruby. This is all about MRI, which is the reference implementation of Ruby.
00:01:19.020 By having this data sheet, we can optionally enable this experimental feature to optimize Ruby itself. Let me explain what is going on behind it.
00:01:31.470 The process starts with Ruby generating a header to be consumed by the JIT compiler. Initially, it works as a C code generator, translating Ruby code to C language.
00:01:52.349 However, merely translating the language itself does not improve performance. When we generate the C code, we need to optimize a variety of aspects.
00:02:06.320 These aspects include inlining instructions, managing variables in cache, and handling method calls. Such optimizations improve performance, rather than simply translating Ruby to C.
00:02:25.440 For simulating Ruby features, we need to call functions within the Ruby interpreter. Thus, translating to C alone won't enhance performance.
00:02:37.240 I will talk about the details of how we can improve this process.
00:02:44.980 After generating C code, it is compiled by a C compiler like GCC, Clang, or Visual Studio. This compiled code can then be linked to a shared library.
00:03:18.370 Because the shared library can be dynamically loaded by the Ruby interpreter using functions like dlopen, many methods generate a lot of data files in a temporary directory.
00:03:39.430 These files can be used for future linking. We link many .so files into one .a file because having many fragmented functions in memory increases overhead.
00:03:54.160 We do this linking in order to reduce overhead on instruction cache.
00:04:09.310 Currently, with Ruby 2.6, I haven't received any segmentation faults because we are running continuous integration for JIT compilers 24 hours a day.
00:04:35.979 It randomly generates segmentation faults, which I have been fixing myself. Now it is somewhat stable.
00:04:55.180 Nonetheless, stability has no meaning if it doesn't improve performance. Let me show the current state of performance for the JIT compiler.
00:05:09.100 The developer teams are creating benchmarks to improve Ruby performance. A popular benchmark is the Ruby 3x3 benchmark, which means Ruby 3 should be three times faster than Ruby 2.0.
00:05:38.530 Currently, after four months of comparing Ruby 2.6 with and without the JIT, it finds that the JIT compiles Ruby to 1.6 times faster. Between Ruby 2.0 and 2.6, the performance is 2.5 times faster.
00:06:05.140 So nearing three times faster is quite feasible with this benchmark. Memory consumption, however, may be a trade-off with speed.
00:06:23.950 In this case, memory consumption appears low because the JIT compiler is a separate process like GCC.
00:06:49.310 The generated code does not consume significant memory either, making its performance promising for Rails as well.
00:07:20.150 However, we're not running any simulators in production; the benchmarks have been conducted on a lighthearted project rather than an actual web application.
00:07:56.290 For real-world solid programs, we need measurements taken in a Rails application. Another famous benchmark for Ruby is the Discourse application.
00:08:24.130 The Discourse application is used by the Ruby community and has been rewritten into a benchmark for Rails performance.
00:08:53.320 Many reports detail performance improvements by measuring Discourse with the JIT compiler. A graph provided by the developer shows that runtime is lower for optimized runs.
00:09:27.030 With Ruby 2.6's performance, memory consumption may seem bad. Nevertheless, I do not wish to focus solely on this presently.
00:09:49.460 The measuring of performance at 10,000 requests does not necessarily reflect actual performance. A real-world application with at least 10 minutes of runtime offers a broader view.
00:10:10.550 Because JIT processing uses the same compiler, if you are currently using Ruby, Puma, or Rails with high CPU utilization, performance degrades.
00:10:33.060 Thus, I am focusing on improving performance after benchmarking has concluded. With all comparisons completed, we aim to ensure that our efforts result in stable improvement.
00:10:48.320 This graph shows throughput. Higher amounts of throughput means better performance.
00:11:02.060 Currently, JIT performance in Ruby 2.6 has been judged less favorable. I am actively working to enhance this situation.
00:11:10.750 My goal is to improve Ruby's performance outcomes significantly, although for now, the Ruby 2.7 JIT shows slight improvement but not enough to exceed the non-JIT performance.
00:11:30.950 The key challenge involves overhead from calling or loading numerous native codes dynamically. I am actively investigating causes for this performance degradation.
00:11:48.010 This presentation details why the JIT is not faster yet and what measures we are taking to improve it. To understand these performance dynamics, we must profile real-world applications and their specific problems.
00:12:23.660 Profiling can be complex, as it impacts various functionalities and logic. It often diverges from core performance concerns, with the Discourse application measurement shedding little light.
00:12:39.970 Currently, I work on improving several aspects of the real-world Rails scaffold usage. This is a crucial area as our real benchmarking should depict realistic usage behavior.
00:13:08.890 In reviewing Rails performance with the Vitamin benchmarking tool, results indicate that while the performance of Ruby 2.6 was slow, there is no significant speed increase with Ruby 2.7 as of yet.
00:13:43.050 However, memory consumption remains steady, with no drastic increase.
00:14:00.260 Further optimization efforts can be expected. Our goal is building compiler-distributed environments, allowing Ruby's JIT performance to improve over time.
00:14:26.420 To conclude, I'm currently focusing on improving Rails performance by continuously measuring through exact benchmarks.
00:14:40.690 The continuous assessment of compiled performance will be crucial moving forward.
00:15:04.370 I have one minute for questions. Feel free to ask.
00:15:09.239 If your question concerns performance outside of allocation, I can share my current analysis.
00:15:22.369 I have observed that close to 15% of time is consumed at the VM level, while about 9% is spent on object allocation or memory management.
00:15:43.680 An additional 6 to 7% can be attributed to regular expression handling. I currently haven't improved the expressions for performance.
00:15:58.630 Essentially, overhead in method calls and optimizations represents an essential area to address in upcoming proceedings.
00:16:05.889 I am open to further questions or discussions after.
00:16:16.919 Thank you!
Takashi Kokubun
@k0kubun
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