From: "ko1 (Koichi Sasada)" <noreply@...>
Date: 2022-04-15T05:42:16+00:00
Subject: [ruby-core:108248] [Ruby master Bug#18733] Ruby always using Performance Cores with Apple M1

Issue #18733 has been updated by ko1 (Koichi Sasada).


Thank you for your report.

On my WSL2 environment with 12 cores, `ruby 3.2.0dev (2022-04-15T04:24:48Z master 92614111c0) [x86_64-linux]` shows worse results.

```
  0.003304   0.000000 102.404055 ( 13.083221)
296.139861 262.090810 558.230671 (278.664518)
```

However, I modified it with 

```ruby
def fib(n)
  return n if n < 2 # `[0,1].include?(n)` generates an Array object
  fib(n-1) + fib(n-2)
end
```

it shows

```
  0.000000   0.003886  31.579734 (  4.092415)
 31.779964   0.003833  31.783797 (  4.114323)
```

maybe because of object allocation (GC) causes contention and the system determines it should not use performance cores.
(BTW I can't see figure "ruby_bug_with_m1")

The conclusion is, the reason of this issue is the implementation of object allocation (GC).


----------------------------------------
Bug #18733: Ruby always using Performance Cores with Apple M1
https://bugs.ruby-lang.org/issues/18733#change-97265

* Author: jakit (Jakit Liang)
* Status: Open
* Priority: Normal
* 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.




-- 
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