[ruby-core:108969] [Ruby master Misc#18834] Significant change in loop speeds (regressing using while loop on ARM chips)

Issue #18834 has been updated by alanwu (Alan Wu).


Interesting! Can you post the output of:

    $ ruby -ve 'pp RbConfig::CONFIG, RubyVM::OPTS'

For your ARM build of Ruby? I suspect the performance difference
could be explained by compiler differences.

----------------------------------------
Misc #18834: Significant change in loop speeds (regressing using while loop on ARM chips)
https://bugs.ruby-lang.org/issues/18834#change-98070

* Author: tarellel (Brandon Hicks)
* Status: Open
* Priority: Normal
----------------------------------------

I was benchmarking some code and one of the benchmarks I came across was <a href="https://github.com/fastruby/fast-ruby/blob/master/code/enumerable/each_with_index-vs-while-loop.rb">fast-ruby's</a> while vs each_with_index. I ran these test multiple times and got very similar results.

Both of these machines benchmarks were ran with ruby v3.1.2.


Intel - i9/32gb Ram (I also ran this on a linux VM or similar specs and got similar results)
ARM - AppleSilicon/32gb Ram


The reason I bring this up, is because most people develop on a Mac and now more than likely on AppleSilicon. But once deployed on a VM or container it's more than likely running on an intel based architecture. I'm kind of curious why there is such a massive change in the loop speeds between the two architectures such as `while` being 31% slower on ARM but also at the same time `each_with_index` is 42% faster.


If someone develops their code on their ARM devises and using the faster of the methods. Once deployed it may run significantly slower than expected because of the architecture speed differences. 



``` shell
# Intel
Warming up --------------------------------------
          While Loop    37.108k i/100ms
     each_with_index    15.900k i/100ms
Calculating -------------------------------------
          While Loop    390.930k (賊 2.3%) i/s -      1.967M in   5.033609s
     each_with_index    158.754k (賊 1.7%) i/s -    795.000k in   5.009286s

Comparison:
          While Loop:   390930.1 i/s
     each_with_index:   158753.7 i/s - 2.46x  (賊 0.00) slower

# ARM
Warming up --------------------------------------
          While Loop    26.594k i/100ms
     each_with_index    27.316k i/100ms
Calculating -------------------------------------
          While Loop    268.372k (賊 0.1%) i/s -      1.356M in   5.053798s
     each_with_index    273.584k (賊 0.2%) i/s -      1.393M in   5.092110s

Comparison:
     each_with_index:   273584.4 i/s
          While Loop:   268371.7 i/s - 1.02x  (賊 0.00) slower
```




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