[ruby-core:102287] [Ruby master Bug#17497] Ractor performance issue

Issue #17497 has been updated by ko1 (Koichi Sasada).


inversion (Yura Babak) wrote in #note-10:
> I also made 2 posts about strange performance testing results (with sources) and some conclusions.
> In my case, 2 ractors work 3-times longer than doing the same payload in the main thread.


With digest benchmark:

```
                               user     system      total        real
serial/26_ruby              0  0.000239   0.000079   2.497317 (  2.503279)
serial/27_ruby              0  0.000972   0.000324   2.306552 (  2.310275)
serial/master_ruby          0  0.000293   0.000098   3.776824 (  3.776623)
serial/ruby                 0  0.000190   0.000063   2.668395 (  2.668287)
r_serial/26_ruby         N/A
r_serial/27_ruby         N/A
r_serial/master_ruby        1  0.000407   0.000000   5.579597 (  5.579969)
r_serial/ruby               1  0.000476   0.000000   2.682626 (  2.683627)
r_parallel/26_ruby       N/A
r_parallel/27_ruby       N/A
r_parallel/master_ruby      1  0.000242   0.000000  48.298173 ( 12.959255)
r_parallel/ruby             1  0.000242   0.000000   3.782164 (  0.984832)
```

seems solved.



----------------------------------------
Bug #17497: Ractor performance issue
https://bugs.ruby-lang.org/issues/17497#change-90142

* Author: marcandre (Marc-Andre Lafortune)
* Status: Closed
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* ruby -v: ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin18]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
There's a strange performance issue with Ractor (at least on MacOS, didn't run on other OS).

I ran a benchmark doing 3 different types of work:
* "fib": method calls (naive fibonacci calculation)
* "cpu": `(0...1000).inject(:+)`
* "sleep": call `sleep`

I get the kind of results I was excepting for the `fib` and for sleeping, but the results for the "cpu" workload show a problem.

It is so slow that my pure Ruby backport (using Threads) is 65x faster  on my Mac Pro (despite having 6 cores). Expected results would be 6x slower, so in that case Ractor is 400x slower than it should 仭

On my MacBook (2 cores) the results are not as bad, the `cpu` workload is 3x faster with my pure-Ruby backport (only) instead of ~2x slower, so the factor is 6x too slow.


```
$ gem install backports
Successfully installed backports-3.20.0
1 gem installed
$ ruby ractor_test.rb
<internal:ractor>:267: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
fib: 110 ms  |  cpu: 22900 ms  |  sleep: 206 ms
$ B=t ruby ractor_test.rb
Using pure Ruby implementation
fib: 652 ms  |  cpu: 337 ms  |  sleep: 209 ms
```

Notice the `sleep` run takes similar time, which is good, and `fib` is ~6x faster on my 6-core CPU (and ~2x faster on my 2-core MacBook), again that's good as the pure ruby version uses Threads and thus runs with a single GVL.

The `cpu` version is the problem.

Script is here: https://gist.github.com/marcandre/bfed626e538a3d0fc7cad38dc026cf0e



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