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Ruby 2.6 JIT / RubyConf 2018
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Takashi Kokubun
November 15, 2018
Programming
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Ruby 2.6 JIT / RubyConf 2018
RubyConf 2018 Los Angeles
Takashi Kokubun
November 15, 2018
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Transcript
Takashi Kokubun @k0kubun Ruby 2.6 JIT
@k0kubun Takashi Kokubun / Arm Ruby Committer for JIT, ERB
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Ruby 2.6
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What's "JIT"?
JIT: Just In Time Compiler
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History of Ruby implementation
def plus(a, b) a + b end + a b
Parse Ruby 1.8 Traverse
def plus(a, b) a + b end + a b
Compile Ruby 1.9~2.5 Interpret getlocal :a getlocal :b send :+
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
How can we use it?
or ruby --jit ... RUBYOPT="--jit" rails s ...
Let's benchmark Ruby 2.6 JIT
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https://gist.github.com/k0kubun/887b9567afa86b326556389ef00e4200
https://gist.github.com/k0kubun/887b9567afa86b326556389ef00e4200 Ruby 2.0: 34.3 Ruby 2.6: 86.7 2.53x faster
https://gist.github.com/k0kubun/887b9567afa86b326556389ef00e4200 Ruby 2.5: 48.3 Ruby 2.6: 86.7 1.80x faster
Achieved Ruby 3x2.5 !!!
How about other benchmarks?
None
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JIT makes things slower?
Today's topic JIT performance characteristics
When does Ruby become slow on JIT?
1. When there are many JIT-ed methods
--jit-max-cache (default: 1000)
JIT by C compiler & dynamic loading
unused space code readonly data 1 method Heap
unused space code readonly data 1 method Heap 2MB (big)
about 4KB ?KB
unused space code readonly data unused space code readonly data
unused space code readonly data 3 methods Heap
unused space code readonly data unused space code readonly data
unused space code readonly data L2, ... cache L1 cache Heap
unused space code readonly data unused space code readonly data
unused space code readonly data L2, ... cache L1 cache Heap
unused space Heap code readonly data unused space code readonly
data unused space code readonly data L2, ... cache L1 cache
2. When there are still methods to be JIT-ed
"JIT compaction"
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"
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
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
CPU/memory resources for C compiler
Locks on GC, waitpid, ...
3. When TracePoint is enabled (to be fixed after Ruby
2.6)
What's TracePoint? When is it enabled? • gem 'web-console' on
your Rails application • byebug or binding.pry (with pry-byebug) • Measuring coverage
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
What is made faster by JIT?
1. Almost all methods
def plus(a, b) a + b end Virtual Machine getlocal
:a getlocal :b send :+ Program Counter Stack Pointer Computer Registers Instruction Pointer
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
2. Basic operators on core classes
VM-optimized methods Integer, Float +, -, *, /, % Array
+, <<, [], []=, empty?, size, length, min, max Hash [], []=, empty?, size, length String +, <<, =~, empty?, size, length, succ common !, !=, ==, <, >, <=, >=
def three 1 + 2 end putobject 1 putobject 2
send :+ JIT mov $0x3,%eax retq Method inlining on JIT
3. Calling Ruby method
Method dispatch on Ruby VM foo.bar
Method dispatch on Ruby VM foo.bar Method search (slow)
Method dispatch on Ruby VM foo.bar Method search (slow) Ruby
method C function attr_reader alias Method entry Foo#bar
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
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?
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?
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
4. Instance variable access
Reading instance variable on VM @foo
Reading instance variable on VM @foo Search index (many branches,
slow)
Reading instance variable on VM @foo Search index (many branches,
slow) self.class. instance_variables[index = 2]
Reading instance variable on VM Search index (many branches, slow)
self.class. instance_variables[index = 2] @foo has cache Verify cache
Reading instance variable on VM Search index (many branches, slow)
self.class. instance_variables[index = 2] @foo different class? has cache Verify cache
Reading instance variable on VM Search index (many branches, slow)
self.class. instance_variables[index = 2] @foo different class? has cache Verify cache
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
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 ✓ ?
Future of Ruby's JIT
Will Ruby 2.6 be fast only on Optcarrot?
Future idea (not for 2.6) • Stack allocation of objects
- That requires "escape analysis" (not easy) - We haven't estimated its possible impact yet
Some rooms for improvements in 2.6 (!?) • Change heuristics
to trigger/compact JIT • Profile-guided optimization • Method inlining
How can we experiment them? Benchmark!
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Create a benchmark for Ruby 3x3?
benchmark_driver.gem
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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!!!