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YJIT Makes Rails
1.7x Faster
@k0kubun
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YJIT Makes Rails
1.7x Faster
@k0kubun
1.8x
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@k0kubun
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Ruby Infra team
paracycle tenderlove eileencodes eightbitraptor peterzhu2118 kddnewton
maximecb XrXr k0kubun nirvdrum rwstauner
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Ruby Infra team
GC Prism
YJIT
Lead
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May 15th - 17th, 2024
NAHA CULTURAL ARTS THEATER NAHArt, Okinawa, Japan
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✦ Production-ready JIT for CRuby
✦ JIT: Just-In-Time Compiler
✦ Speeds up methods that are called 30+ times
YJIT
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Shopify StoreFront
Ruby 3.3 YJIT vs Interpreter
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✦ --yjit
✦ RUBY_YJIT_ENABLE=1
✦ RubyVM::YJIT.enable (Ruby 3.3+)
✦ Rails 7.2 will call this in a default initializer
Enabling YJIT
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✦ --yjit-exec-mem-size
✦ Default: 48MiB (since Ruby 3.3.1)
✦ tip: Try 32MiB, 24MiB, or 16MiB
✦ YJIT uses 3-4x of --yjit-exec-mem-size
✦ 2-3x is used for metadata
Minimizing YJIT's memory usage
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May 15th - 17th, 2024
NAHA CULTURAL ARTS THEATER NAHArt, Okinawa, Japan
Ruby 3.3 (and 3.4)
YJIT optimizations
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✦ What is the most impactful Ruby 3.3 YJIT optimization?
✦ The PR made Railsbench 7% faster
Ruby 3.3 YJIT optimizations
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May 15th - 17th, 2024
NAHA CULTURAL ARTS THEATER NAHArt, Okinawa, Japan
Method Call Fallbacks
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def foo(a)
@foo = bar(a)
end
Ruby Code
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def foo(a)
@foo = bar(a)
end
Ruby Code
putself
getlocal :a
send :bar
dup
setivar @foo
leave
Ruby VM
Instructions
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def foo(a)
@foo = bar(a)
end
Ruby Code
putself
getlocal :a
send :bar
dup
setivar @foo
leave
Ruby VM
Instructions JIT Code
jit_putself
jit_getlocal :a
jit_send :bar
jit_dup
jit_setivar @foo
jit_leave
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def foo(a)
@foo = bar(a)
end
Ruby Code
putself
getlocal :a
send :bar
dup
setivar @foo
leave
Ruby VM
Instructions JIT Code
JIT: 100%
jit_putself
jit_getlocal :a
jit_send :bar
jit_dup
jit_setivar @foo
jit_leave
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def foo(a)
@foo = bar(**a)
end
Ruby Code
putself
getlocal :a
send :bar, **
dup
setivar @foo
leave
Ruby VM
Instructions
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def foo(a)
@foo = bar(**a)
end
Ruby Code
putself
getlocal :a
send :bar, **
dup
setivar @foo
leave
Ruby VM
Instructions JIT Code
jit_putself
jit_getlocal :a
side_exit
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def foo(a)
@foo = bar(**a)
end
Ruby Code
putself
getlocal :a
send :bar, **
dup
setivar @foo
leave
Ruby VM
Instructions JIT Code
jit_putself
jit_getlocal :a
side_exit
JIT: 33% Interpreter: 67%
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def foo(a)
@foo = bar(**a)
end
Ruby Code
putself
getlocal :a
send :bar, **
dup
setivar @foo
leave
Ruby VM
Instructions JIT Code
jit_putself
jit_getlocal :a
vm_send :bar
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def foo(a)
@foo = bar(**a)
end
Ruby Code
putself
getlocal :a
send :bar, **
dup
setivar @foo
leave
Ruby VM
Instructions JIT Code
JIT: 100%
jit_putself
jit_getlocal :a
vm_send :bar
jit_dup
jit_setivar @foo
jit_leave
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✦ Ruby 3.3: Use the interpreter’s C function (like MJIT) for:
✦ Unsupported calls
✦ Megamorphic calls
✦ Fallbacks allow the subsequent code to be compiled
Method Call Fallbacks
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✦ Ruby 3.3: Use the interpreter’s C function (like MJIT) for:
✦ Unsupported calls
✦ Megamorphic calls ← What’s this?
✦ Fallbacks allow the subsequent code to be compiled
Method Call Fallbacks
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class X
def call
@x = x
end
end
class A < X
def x = :a
end
:a if self.class == A
Ruby
Code
Ruby 3.2 YJIT
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class X
def call
@x = x
end
end
class A < X
def x = :a
end
class B < X
def x = :b
end
:a if self.class == A
Ruby
Code
Ruby 3.2 YJIT
:b if self.class == B
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class X
def call
@x = x
end
end
class A < X
def x = :a
end
class B < X
def x = :b
end
class C < X
def x = :c
end
:a if self.class == A
Ruby
Code
Ruby 3.2 YJIT
:b if self.class == B
:c if self.class == C
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class X
def call
@x = x
end
end
class A < X
def x = :a
end
class B < X
def x = :b
end
class C < X
def x = :c
end
class D < X
def x = :d
end
:a if self.class == A
Ruby
Code
Ruby 3.2 YJIT
:b if self.class == B
:c if self.class == C
side exit
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class X
def call
@x = x
end
end
class A < X
def x = :a
end
class B < X
def x = :b
end
class C < X
def x = :c
end
class D < X
def x = :d
end
:a if self.class == A
Ruby
Code
Ruby 3.2 YJIT
:b if self.class == B
:c if self.class == C
side exit
:a if self.class == A
:b if self.class == B
:c if self.class == C
vm_send :x
Ruby 3.3 YJIT
setivar @x
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May 15th - 17th, 2024
NAHA CULTURAL ARTS THEATER NAHArt, Okinawa, Japan
Exception Handlers
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✦ In CRuby, exception handlers are executed differently
from regular methods
✦ Ruby 3.3 YJIT added support for them in CRuby JITs for
the first time
✦ "Exceptions" are not necessarily Ruby exceptions, e.g.
break/return in blocks
Exception Handlers
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def foo(arr)
@foo = arr.each do |a|
break a if a.odd?
end
end
Ruby 3.2
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def foo(arr)
@foo = arr.each do |a|
break a if a.odd?
end
end
getlocal arr
send :each, block
dup
setivar @foo
leave
getlocal a
send :odd?
branchunless L0
getlocal a
throw TAG_BREAK
leave
L0: putnil
leave
Ruby 3.2
Call Stack
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def foo(arr)
@foo = arr.each do |a|
break a if a.odd?
end
end
getlocal arr
send :each, block
dup
setivar @foo
leave
getlocal a
send :odd?
branchunless L0
getlocal a
throw TAG_BREAK
leave
L0: putnil
leave
Call Stack
Ruby 3.2
foo
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def foo(arr)
@foo = arr.each do |a|
break a if a.odd?
end
end
getlocal arr
send :each, block
dup
setivar @foo
leave
getlocal a
send :odd?
branchunless L0
getlocal a
throw TAG_BREAK
leave
L0: putnil
leave
Call Stack
Ruby 3.2
foo
Array#each
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def foo(arr)
@foo = arr.each do |a|
break a if a.odd?
end
end
getlocal arr
send :each, block
dup
setivar @foo
leave
getlocal a
send :odd?
branchunless L0
getlocal a
throw TAG_BREAK
leave
L0: putnil
leave
Call Stack
Ruby 3.2
foo
Array#each
block in foo
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def foo(arr)
@foo = arr.each do |a|
break a if a.odd?
end
end
getlocal arr
send :each, block
dup
setivar @foo
leave
getlocal a
send :odd?
branchunless L0
getlocal a
throw TAG_BREAK
leave
L0: putnil
leave
Call Stack
Ruby 3.2
foo
Array#each
block in foo
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def foo(arr)
@foo = arr.each do |a|
break a if a.odd?
end
end
getlocal arr
send :each, block
dup
setivar @foo
leave
getlocal a
send :odd?
branchunless L0
getlocal a
throw TAG_BREAK
leave
L0: putnil
leave
Call Stack
Ruby 3.2
foo
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def foo(arr)
@foo = arr.each do |a|
break a if a.odd?
end
end
getlocal arr
send :each, block
dup
setivar @foo
leave
getlocal a
send :odd?
branchunless L0
getlocal a
throw TAG_BREAK
leave
L0: putnil
leave
Ruby 3.2
JIT: 60%
Interpreter: 40%
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def foo(arr)
@foo = arr.each do |a|
break a if a.odd?
end
end
getlocal arr
send :each, block
dup
setivar @foo
leave
getlocal a
send :odd?
branchunless L0
getlocal a
throw TAG_BREAK
leave
L0: putnil
leave
Ruby 3.3
JIT: 100%
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May 15th - 17th, 2024
NAHA CULTURAL ARTS THEATER NAHArt, Okinawa, Japan
Register Allocator
for Stack Values
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✦ Ruby 3.2 YJIT writes VM stack values onto memory
✦ Ruby 3.3 YJIT allocates registers for them
Register Allocator for Stack Values
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def three
1 + 2
end
Ruby 3.2
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.2
Memory
Register A Register B
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.2
Memory
Register A Register B
1
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.2
Memory
Register A Register B
1
2
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.2
Memory
Register A Register B
3
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.2
Memory
Register A Register B
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.3
Memory
Register A Register B
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.3
Memory
Register A Register B
1
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.3
Memory
Register A Register B
1 2
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.3
Memory
Register A Register B
3
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def three
1 + 2
end
putobject 1
putobject 2
opt_plus
leave
Ruby 3.3
Memory
Register A Register B
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✦ Ruby 3.4 YJIT: Optimize local variables like stack values,
speculating Kernel#binding is not called
✦ Ruby 3.4 will hopefully allocate registers for them too
(under development)
Register Allocator for Local Variables
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May 15th - 17th, 2024
NAHA CULTURAL ARTS THEATER NAHArt, Okinawa, Japan
Method Inlining for Ruby
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✦ YJIT 3.3+ inlines single-line methods that return:
✦ Ruby 3.3: 1, 2, 3, …, true, false, nil, :symbol
✦ Ruby 3.4: self, local variables
Method Inlining for Ruby
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Active
Support
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Active
Support
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Active
Support
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Symbol#to_sym
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Sorbet Helper Patches
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May 15th - 17th, 2024
NAHA CULTURAL ARTS THEATER NAHArt, Okinawa, Japan
Method Inlining for C
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✦ Ruby 3.3 YJIT specializes many C methods, which leads
to a high C method inlining ratio
✦ Ruby 3.4 YJIT pushes "lazy frames"
Method Inlining for C
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✦ Enable YJIT in production now!
✦ YJIT speeds up production apps by 10-20%
✦ Upgrade Ruby to 3.3
✦ JIT more code, allocate registers, and inline method calls
Conclusion