From: "jhawthorn (John Hawthorn) via ruby-core" <ruby-core@...>
Date: 2025-12-11T18:53:58+00:00
Subject: [ruby-core:124154] [Ruby Bug#18733] Heavy GC allocations cause performance issue with Ractor

Issue #18733 has been updated by jhawthorn (John Hawthorn).


Just to update that though GC is still global more progress has been made. I'm on a new PC, so rerunning the benchmark against the old SHA.

```
��� ruby -v
ruby 3.5.0dev (2025-07-02T20:01:24Z v4.0.0-preview2~2697 d5f5a56bf2) +PRISM [x86_64-linux]
��� ruby -W0 test.rb
  0.000000   0.001562  28.821554 (  3.660323)
 31.873376   3.184418  35.057794 ( 12.195926)
```

```
��� ruby -v
ruby 4.0.0dev (2025-12-11T17:53:18Z master 89e09e4daf) +PRISM [x86_64-linux]
��� ruby test.rb
  0.001531   0.000000  26.558190 (  3.387530)
 31.540110   1.433400  32.973510 (  8.224187)
```

----------------------------------------
Bug #18733: Heavy GC allocations cause performance issue with Ractor
https://bugs.ruby-lang.org/issues/18733#change-115612

* Author: jakit (Jakit Liang)
* Status: Assigned
* Assignee: ractor
* ruby -v: ruby 3.1.1p18 (2022-02-18 revision 53f5fc4236) [arm64-darwin21]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
Code:

```
require 'benchmark'

def fib(n)
  return n if [0,1].include?(n)
  fib(n-1) + fib(n-2)
end

tp = []

puts Benchmark.measure {
  8.times do
    tp << fork { fib(37) }
  end

  tp.each { |t| Process.wait(t) }
}

puts Benchmark.measure {
  8.times.map {
    Ractor.new { fib(37) }
  }.each{ |r| r.take }
}
```

Result:

|A |B |
|--|--|
| fork | 0.000264   0.003439  87.181198 ( 11.211349) |
| Ractor | 80.292916  15.062559  95.355475 ( 39.569527) |

And I found that here's the problem showing on the ActiveMonitor.app:

![ruby_bug_with_m1](http://jakit.cn/screen_shot_ruby_bug.jpg)

As you can see, the process of ruby is always using all Performance Cores on my Apple M1 Mac.

But there's no one of the Efficiency Cores was in used by ruby Ractor.




-- 
https://bugs.ruby-lang.org/
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