Ruby 2.6 JIT / RubyConf 2018

RubyConf 2018 Los Angeles

Transcript

1. Takashi Kokubun @k0kubun Ruby 2.6 JIT
2. @k0kubun Takashi Kokubun / Arm Ruby Committer for JIT, ERB
7. Ruby 2.6
9. What's "JIT"?
10. JIT: Just In Time Compiler
12. History of Ruby implementation
13. def plus(a, b) a + b end + a b Parse Ruby 1.8 Traverse
14. def plus(a, b) a + b end + a b Compile Ruby 1.9~2.5 Interpret getlocal :a getlocal :b send :+
15. def plus(a, b) a + b end + a b JIT Ruby 2.6 (New!) Execute getlocal :a getlocal :b send :+ mov %rdi,%rdx mov %rsi,%rax add %rdx,%rax
16. How can we use it?
17. or ruby --jit ... RUBYOPT="--jit" rails s ...
18. Let's benchmark Ruby 2.6 JIT
20. https://gist.github.com/k0kubun/887b9567afa86b326556389ef00e4200
21. https://gist.github.com/k0kubun/887b9567afa86b326556389ef00e4200 Ruby 2.0: 34.3 Ruby 2.6: 86.7 2.53x faster
22. https://gist.github.com/k0kubun/887b9567afa86b326556389ef00e4200 Ruby 2.5: 48.3 Ruby 2.6: 86.7 1.80x faster
23. Achieved Ruby 3x2.5 !!!
24. How about other benchmarks?
27. JIT makes things slower?
28. Today's topic JIT performance characteristics
29. When does Ruby become slow on JIT?
30. 1. When there are many JIT-ed methods
31. --jit-max-cache (default: 1000)
32. JIT by C compiler & dynamic loading
33. unused space code readonly data 1 method Heap
34. unused space code readonly data 1 method Heap 2MB (big) about 4KB ?KB
35. unused space code readonly data unused space code readonly data unused space code readonly data 3 methods Heap
36. unused space code readonly data unused space code readonly data unused space code readonly data L2, ... cache L1 cache Heap
37. unused space code readonly data unused space code readonly data unused space code readonly data L2, ... cache L1 cache Heap
38. unused space Heap code readonly data unused space code readonly data unused space code readonly data L2, ... cache L1 cache
39. 2. When there are still methods to be JIT-ed
40. "JIT compaction"
41. unused space code readonly data unused space code readonly data unused space code readonly data When it reaches --jit-max-cache, it fires "JIT compaction"
42. unused space code readonly data unused space code readonly data unused space code readonly data unused space code code code readonly data readonly data readonly data
43. unused space code readonly data unused space code readonly data unused space code readonly data unused space code code code readonly data readonly data readonly data L2, ... cache
44. CPU/memory resources for C compiler
45. Locks on GC, waitpid, ...
46. 3. When TracePoint is enabled (to be fixed after Ruby 2.6)
47. What's TracePoint? When is it enabled? • gem 'web-console' on your Rails application • byebug or binding.pry (with pry-byebug) • Measuring coverage
48. Summary: When JIT makes Ruby slow Optcarrot Rails 1. When there are many JIT-ed methods ✓ 2. When there are still methods to be JIT-ed (Is it a short benchmark?) ✓ 3. When TracePoint is enabled
49. What is made faster by JIT?
50. 1. Almost all methods
51. def plus(a, b) a + b end Virtual Machine getlocal :a getlocal :b send :+ Program Counter Stack Pointer Computer Registers Instruction Pointer
52. def plus(a, b) a + b end Virtual Machine getlocal :a getlocal :b send :+ Program Counter Stack Pointer Computer JIT Instruction Pointer Registers mov %rdi,%rdx mov %rsi,%rax add %rdx,%rax
53. 2. Basic operators on core classes
54. VM-optimized methods Integer, Float +, -, *, /, % Array +, <<, [], []=, empty?, size, length, min, max Hash [], []=, empty?, size, length String +, <<, =~, empty?, size, length, succ common !, !=, ==, <, >, <=, >=
55. def three 1 + 2 end putobject 1 putobject 2 send :+ JIT mov $0x3,%eax retq Method inlining on JIT
56. 3. Calling Ruby method
57. Method dispatch on Ruby VM foo.bar
58. Method dispatch on Ruby VM foo.bar Method search (slow)
59. Method dispatch on Ruby VM foo.bar Method search (slow) Ruby method C function attr_reader alias Method entry Foo#bar
60. Method dispatch on Ruby VM foo.bar Method search (slow) Verify cache Ruby method C function attr_reader alias Method entry Foo#bar has cache
61. Method dispatch on Ruby VM foo.bar Method search (slow) Verify cache Ruby method C function attr_reader alias Method entry Foo#bar has cache redefined?
62. Method dispatch on Ruby VM foo.bar Method search (slow) Verify cache Ruby method C function attr_reader alias Method entry Foo#bar has cache redefined?
63. Method dispatch on JIT foo.bar Verify cache Ruby method Method entry Foo#bar has cache Cancel JIT! Less branches Less memory access redefined? some inlining
64. 4. Instance variable access
65. Reading instance variable on VM @foo
66. Reading instance variable on VM @foo Search index (many branches, slow)
67. Reading instance variable on VM @foo Search index (many branches, slow) self.class. instance_variables[index = 2]
68. Reading instance variable on VM Search index (many branches, slow) self.class. instance_variables[index = 2] @foo has cache Verify cache
69. Reading instance variable on VM Search index (many branches, slow) self.class. instance_variables[index = 2] @foo different class? has cache Verify cache
70. Reading instance variable on VM Search index (many branches, slow) self.class. instance_variables[index = 2] @foo different class? has cache Verify cache
71. Reading instance variable on JIT self.class. instance_variables[2] @foo different class? has cache Verify cache Cancel JIT! inlined index Less branches Less memory access
72. Summary: When JIT makes Ruby fast Optcarrot Rails 1. Almost all methods ✓ ✓ 2. Basic operators on core classes ✓ 3. Calling Ruby method ✓ ✓ 4. Instance variable access ✓ ?
73. Future of Ruby's JIT
74. Will Ruby 2.6 be fast only on Optcarrot?
75. Future idea (not for 2.6) • Stack allocation of objects - That requires "escape analysis" (not easy) - We haven't estimated its possible impact yet
76. Some rooms for improvements in 2.6 (!?) • Change heuristics to trigger/compact JIT • Profile-guided optimization • Method inlining
77. How can we experiment them? Benchmark!
80. Create a benchmark for Ruby 3x3?
81. benchmark_driver.gem
86. Conclusion • Ruby 2.6.0-preview3 JIT is still early days - Small --jit-max-cache might be an option for now • We still have chance to make Ruby 2.6.0 better - Benchmarks are wanted!!!