How to use the Ruby 2.6 Just-in-Time (JIT) Compiler

Summary

In this video, the speaker discusses how to enable and run Ruby 2.6's experimental Just-In-Time (JIT) compiler. While JIT offers a significant speed boost for specific benchmarks, like the opt karat emulator, it's not yet effective for memory-heavy applications like Rails or Sidekiq. The speaker walks developers through enabling JIT using Ruby commands and environment variables and highlights the importance of testing performance in their own applications. As JIT is still experimental, it's not recommended for production environments yet, but the speaker encourages users to explore its potential as improvements are made in future releases.

Takeaways

• 😀 Ruby 2.6 introduces an experimental Just-In-Time (JIT) compiler to improve performance.
• 😀 JIT is not recommended for production environments, especially for memory-intensive applications like Rails or Sidekick.
• 😀 The JIT compiler improves performance significantly for CPU-heavy tasks, like benchmarks such as opt karat, an NES emulator.
• 😀 Ruby 2.6's JIT can speed up some workloads by up to 1.7 times, especially in benchmark scenarios.
• 😀 The JIT feature is disabled by default in Ruby 2.6 to avoid negatively impacting production code.
• 😀 To enable JIT in Ruby 2.6, use the `--jit` flag when running Ruby scripts.
• 😀 To see detailed logs of JIT compilation, use the `--jit-verbose=1` flag along with the `--jit` flag.
• 😀 For Rails or Sidekick, set the `RUBYOPT` environment variable to `--jit` to enable JIT for these applications.
• 😀 It's important to benchmark your code with and without JIT enabled to assess its impact on performance.
• 😀 Future releases of Ruby may improve JIT for memory-intensive applications, allowing better performance for Rails and Sidekick.

Q & A

What is the major new feature introduced in Ruby 2.6?

The major new feature in Ruby 2.6 is the Just-In-Time (JIT) compiler, which is designed to improve the performance of Ruby code by compiling parts of the code at runtime.

Is the JIT compiler in Ruby 2.6 fully stable and ready for production use?

No, the JIT compiler in Ruby 2.6 is still experimental, and it is not recommended to use it in production environments just yet.

What kind of performance improvements can the JIT compiler provide?

The JIT compiler can offer substantial performance improvements for CPU-intensive tasks. For example, a benchmark using the 'opt karat' NES emulator showed a 1.7x performance increase.

Does the JIT compiler improve performance for memory-intensive applications like Rails?

Currently, the JIT compiler does not offer significant improvements for memory-intensive applications like Rails or Sidekiq.

How can you enable the JIT compiler for a Ruby script?

To enable the JIT compiler for a Ruby script, you can use the following command: `ruby --jit your_script.rb`.

How can you check if JIT is enabled and view detailed JIT logs?

To check if JIT is enabled and view detailed logs, you can use the command: `RUBY_JIT_VERBOSE=1 ruby --jit your_script.rb`.

How can you enable JIT for Rails or other Ruby applications run via executables like `bundle exec`?

For Rails and other Ruby applications, you can enable JIT by setting the `RUBY_OPT` environment variable: `export RUBY_OPT='--jit'`.

Why is the JIT compiler disabled by default in Ruby 2.6?

The JIT compiler is disabled by default in Ruby 2.6 to prevent performance degradation in production applications, especially for memory-intensive tasks like Rails, where it has not shown significant improvements.

What should developers do to determine if JIT improves performance for their code?

Developers should benchmark their own code with JIT enabled and disabled to determine if it offers a performance benefit for their specific use case.

What future improvements are expected for the JIT compiler in Ruby?

Ruby's development team is working on improving the JIT compiler, particularly for memory-heavy applications like Rails, with the goal of achieving even greater performance improvements in future releases.