Exit(ing) through the YJIT

When optimizing code for the YJIT compiler it can be difficult to figure out what code is exiting and why. While working on tracing exits in a Ruby codebase, I found myself wishing we had a tool to reveal the exact line that was causing exits to occur. We set to work on building that functionality into Ruby and now we are able to see every side-exit and why. In this talk we’ll learn about side-exits and how we built a tracer for them. We’ll explore the original implementation, how we rewrote it in Rust, and lastly why it’s so important to always ask "can I make what I built even better?"

Transcript

1. EXIT(ing) Through the YJIT
3. Eileen M. Uchitelle Twitter / GitHub: @eileencodes Mastadon: @eileencodes@ruby.social
6. EXIT(ing) Through the YJIT
7. What is a JIT?
8. What is a JIT? "Just in time" compiler
9. MJIT "Method-Based" JIT
10. YJIT "Yet Another" JIT
12. def call_method(arg) if arg == "hello" puts arg else puts "bye" end end YJIT only compiles code that is run
13. def call_method(arg) if arg == "hello" puts arg else puts "bye" end end call_method("hello") YJIT only compiles code that is run
14. def call_method(arg) if arg == "hello" puts arg else puts "bye" end end call_method("hello") YJIT only compiles code that is run
15. def call_method able_to_compile not_able_to_compile end call_method YJIT can compile parts of methods
16. def call_method able_to_compile not_able_to_compile end call_method YJIT can compile parts of methods
17. def call_method able_to_compile not_able_to_compile end call_method YJIT can compile parts of methods
18. How is YJIT implemented?
19. MJIT vs YJIT Which to use?
20. How can I use YJIT?
21. $ docker pull rubylang/ruby:master-debug- nightly-focal Docker Images
22. Pre-requisites • autoconf • make • bison • GCC or Clang • libyaml • openssl@1.1 • Rust (for YJIT) • Ruby
23. Run autogen $ cd ruby $ ./autogen.sh
24. Configure Ruby $ ./configure --prefix=~/.rubies/ruby-yjit --with-openssl-dir=$(brew --prefix openssl@1.1) --disable-install-doc
25. Configure Ruby: Set prefix $ ./configure --prefix=~/.rubies/ruby-yjit --with-openssl-dir=$(brew --prefix openssl@1.1) --disable-install-doc
 

26. Configure Ruby: openssl $ ./configure --prefix=~/.rubies/ruby-yjit --with-openssl-dir=$(brew --prefix openssl@1.1) --disable-install-doc
27. Configure Ruby: Disable rdoc $ ./configure --prefix=~/.rubies/ruby-yjit --with-openssl-dir=$(brew --prefix openssl@1.1) --disable-install-rdoc
 

28. Install Ruby $ make install
29. $ RUBY_YJIT_ENABLE=1 ruby my_script.rb $ ruby --yjit my_script.rb $ ruby --jit my_script.rb Enabling YJIT
30. YJIT dev mode $ ./configure --enable-yjit=dev --prefix=~/.rubies/ruby-yjit --with-openssl-dir=$(brew --prefix openssl@1.1) $ make install
31. "Exit" When YJIT is unable to compile
32. ar_demo.rb ActiveRecord::Base.establish_connection( adapter: "sqlite3", database: ":memory:") ActiveRecord::Schema.define do create_table :posts, force: true do |t| end end class Post < ActiveRecord::Base end class BugTest < ActiveSupport::TestCase def test_create Post.create! end end
33. Running with stats enabled $ bundle exec ruby --yjit-stats ar_demo.rb
38. But what does the code look like?
39. "We can totally make that work." - Aaron Patterson
40. Tracing YJIT Exits
42. Tracing exits $ bundle exec ruby --yjit-trace-exits ar_demo.rb
47. ar_demo.rb [...] class Post < ActiveRecord::Base def call_method(options) one, two, three = options end end class BugTest < ActiveSupport::TestCase def test_create post = Post.create! post.call_method("hello") end end
48. Fixing broken code $ bundle exec ruby --yjit-trace-exits --yjit-call-threshold=1 ar_demo.rb
52. How will we use this?
53. Optimizing YJIT
54. yjit/src/codegen.rs /// Maps a YARV opcode to a code generation function (if supported) fn get_gen_fn(opcode: VALUE) -> Option<InsnGenFn> { let VALUE(opcode) = opcode; let opcode = opcode as ruby_vminsn_type; assert!(opcode < VM_INSTRUCTION_SIZE); match opcode { [...] YARVINSN_send => Some(gen_send), YARVINSN_invokeblock => Some(gen_invokeblock), YARVINSN_invokesuper => Some(gen_invokesuper), YARVINSN_leave => Some(gen_leave), [...]
55. yjit/src/codegen.rs /// Maps a YARV opcode to a code generation function (if supported) fn get_gen_fn(opcode: VALUE) -> Option<InsnGenFn> { let VALUE(opcode) = opcode; let opcode = opcode as ruby_vminsn_type; assert!(opcode < VM_INSTRUCTION_SIZE); match opcode { [...] YARVINSN_send => Some(gen_send), YARVINSN_invokeblock => Some(gen_invokeblock), YARVINSN_invokesuper => Some(gen_invokesuper), YARVINSN_leave => Some(gen_leave), [...]
56. yjit/src/codegen.rs asm.jne( counted_exit!( ocb, side_exit, invokesuper_block ).into() );
57. Optimizing our Ruby Code
58. Try YJIT on your app!
59. Help us improve YJIT
60. Eileen M. Uchitelle Twitter / GitHub: @eileencodes Mastadon: @eileencodes@ruby.social