[ruby-core:106959] [Ruby master Bug#18454] YJIT slowing down key Discourse benchmarks

Issue #18454 has been updated by byroot (Jean Boussier).


What about YJIT_STATS=1 ? That's the part that will tell us why it's slower.

> Oddly bootsnap may be causing an RSS increase 338 -> 370 (on 2.7.5 290 -> 315)

RSS isn't necessarily the best mesure, but yes bootsnap incur increased memory usage for its load path index. A couple years ago I had some ideas to drop the index at the end of the boot process, I'll try look into it when I get back to work next week, fell free to open an issue on Shopify/bootsnap. 

> fiber.so: undefined symbol: ruby_Init_Fiber_as_Coroutin

From `3.1.0` with just the backport? Sounds weird, something must have gone wrong during compilation.

> 3.2 is going to be a rough upgrade it seems, the File.exists deprecation is going to be very rough

Meh, we test ruby-head nightly, so I'll likely open PRs about it on popular gems. And for private code it's just a search and replace, no big deal. Also it's just a warning, you can turn it off easily until your dependencies are fixed.

----------------------------------------
Bug #18454: YJIT slowing down key Discourse benchmarks
https://bugs.ruby-lang.org/issues/18454#change-95782

* Author: sam.saffron (Sam Saffron)
* Status: Open
* Priority: Normal
* ruby -v: 3.1.0p0
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------

4 out of 6 key Discourse benchmarks used in: https://github.com/discourse/discourse/blob/main/script/bench.rb are slower under YJIT. 

Vanilla (median) -> YJIT (median)

Categories: 47ms -> 51
Home page: 85 -> 86
Topic: 42 -> 38
Categories Admin: 48 -> 50
Home Admin: 83 -> 84
Topic Admin: 43 -> 39
Boot: 1740ms -> 2484ms 
RSS: 358756 -> 640540

This was run with a simple `RUBYOPT='--enable-yjit' ruby script/bench.rb -i 100 -s`


To get Discourse working with Ruby 3.1 you will need: 



```
diff --git a/Gemfile b/Gemfile
index 9cdfbf21a9..403c428718 100644
--- a/Gemfile
+++ b/Gemfile
@@ -263,3 +263,11 @@ gem 'colored2', require: false
 gem 'maxminddb'
 
 gem 'rails_failover', require: false
+
+if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("3.0.0")
+  gem 'net-pop', require: false
+  gem 'net-smtp', require: false
+  gem 'net-imap', require: false
+  # waiting on new version of i18n gem
+  gem 'psych', '3.3.2'
+end
```


It is clear that memory usage and boot time have to take a hit here, but slowing down home page seems concerning. Any ideas on what we should test here and how to narrow this down? 



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