Bug #20634: ruby uses 1/2 (7 out of 16) cores for 16 ractors with RUBY_MAX_CPU=16 environment variable set - Ruby master - Ruby Issue Tracking System

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Bug #20634

closed

Status:

Closed

Assignee:

Target version:

ruby -v:

ruby 3.3.1 (2024-04-23 revision c56cd86388) [x86_64-linux]

Backport:

Description

It's a cont for #20618, feel free to close this one and reopen the original bug.

According to top, the below code uses 7/16 cores (700%) of my AMD Ryzen 7 5800HS:

#!/usr/bin/env ruby

16.times {
  Ractor.new {
    10_000.downto(1) { |i|
      100_000.downto(1) { |j|
        i * j
      }
    }
  }
}

sleep 30

Command I ran was RUBY_MAX_CPU=16 ruby test.rb. Adding RUBY_MN_THREADS=1 increases CPU usage to 8 cores, possibly due to N:M for the main Ractor.

The same code occupies all 16 cores on ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]

The problem reproduces on ruby 3.3.3 (2024-06-12 revision f1c7b6f435) [x86_64-linux] (ruby from the latest docker image).

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