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Towards Ruby 4 JIT
@k0kubun
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@k0kubun
Maintain: MJIT, Haml, ERB
Shopify team
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GitHub Sponsors
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Haml 6
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Introduction to Ruby JIT
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How does Ruby JIT work?
Ruby
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How does Ruby JIT work?
1
+
2
Ruby
Abstract
Syntax
Tree
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How does Ruby JIT work?
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+
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putobject 1
putobject 2
opt_plus
leave
Ruby
Abstract
Syntax
Tree
Instruction
Sequence
(Bytecode)
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How does Ruby JIT work?
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+
2
putobject 1
putobject 2
opt_plus
leave
Ruby
Abstract
Syntax
Tree
Instruction
Sequence
(Bytecode)
Machine
Code
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How does Ruby JIT work?
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CRuby JIT 1: MJIT
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CRuby JIT 2: YJIT
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Current CRuby JITs
speed.yjit.org
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Current CRuby JITs
speed.yjit.org
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Current CRuby JITs
• YJIT
• Available since Ruby 3.1
• --jit or --yjit
• MJIT
• Available since Ruby 2.6
• --mjit
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Current CRuby JITs
• YJIT
• Ruby 3.1: x86_64 only, no code GC, written in C
• Ruby 3.2: arm64 support, (hopefully) code GC, written in Rust
• MJIT
• Ruby 3.1: Stable-ish, portable, native threads, written in C
• Ruby 3.2: Experimental, fork + SIGCHLD, written in Ruby
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MJIT in Ruby
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mjit.rb: Secret "standard library" in Ruby 3.2
• mjit.rb
• Even more powerful than TracePoint
• You can monkey-patch CRuby JIT
• No compatibility guarantee
• Every module is private, so const_get is required
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BYOJ: Bring Your Own JIT
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BYOJ: Bring Your Own JIT
• Load and pause MJIT with --mjit=pause
• Define RubyVM::MJIT.compile
• Use RubyVM::MJIT.const_get(:C) to hack RubyVM
• Call RubyVM::MJIT.resume to start JIT
With Ruby 3.2:
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YJIT-style JIT
• Monkey-patch RubyVM::MJIT.compile
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MJIT-style JIT
• Monkey-patch RubyVM::MJIT::Compiler.compile
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MJIT-style JIT
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Everyone is writing CRuby JIT
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Benchmarking Ruby JIT
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yjit-bench
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yjit-bench
• yjit-bench has three kinds of benchmarks:
1. Headlining Benchmarks
2. Other Benchmarks
3. Micro Benchmarks
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1. Headlining benchmarks
• activerecord
• hexapdf
• liquid-render
• mail
• psych-load
• railsbench
✉
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2. Other Benchmarks
• binarytrees, fankuchredux, nbody
• chunky_png
• erubi, erubi_rails
• lee
• optcarrot
• rubykon
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3. Micro Benchmarks
• 30k_ifelse, 30k_methods
• cfunc_itself, str_concat
• fib
• getivar, setivar
• keyword_args
• respond_to
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Benchmark Your Own JIT
• ./run_benchmarks.rb -e “/path/to/ruby --any-option”
• Pass multiple -e options to compare different JITs
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Towards Ruby 4 JIT
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My wish on Ruby 4 JIT
• I want Ruby 4 to be as fast as Java or JavaScript
• Ruby 4's performance should be a reason to leave Python
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More Concrete Examples
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Ruby 4 Canary
• true is mov-ed (immediate)
• No opt_* VM instruction
• Constant folding
• Ruby / C method inlining
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Ruby 4 Canary’
• Single branch instruction
to access @one
• Single register to access
two
• No heap allocation
• No stack frame
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Ruby 4 Canary 2
• 5000050000 is mov-ed
(immediate)
• Ruby -> C -> Ruby inlining
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How can we get there?
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Optimization Challenges
1. Constants
2. Variables
3. Method calls
4. Garbage collection
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1. Constants
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1. Constants
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1. Constants
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1. Constants
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1. Constants
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1. Constants
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1. Constants
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1. Constants
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2. Variables
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2. Variables
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2. Variables
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2. Variables
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2. Variables
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2. Variables
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2. Variables
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2. Variables
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2. Variables
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2. Variables
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2. Variables
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2. Variables
2021 2022 (tomorrow)
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3. Method calls
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3. Method calls
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3. Method calls
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3. Method calls
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3. Method calls
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3. Method calls
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3. Method calls
• Code locality
• Method inlining: C 㱻 Ruby
• Pass arguments with native ABI
• Deoptimization on redefinition or interruption (or TracePoint)
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4. Garbage collection
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4. Garbage collection
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4. Garbage collection
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Next Steps
• We still have a lot of rooms for improvements on yjit-bench
• More cross-instruction optimizations
• More method inlining over Ruby and C
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Conclusion
• Build your own JIT with Ruby 3.2
• Benchmark your JIT with yjit-bench