From: takashikkbn@...
Date: 2020-12-08T03:21:29+00:00
Subject: [ruby-core:101301] [Ruby master Bug#17373] Ruby 3.0 is slower at Discourse bench than Ruby 2.7

Issue #17373 has been updated by k0kubun (Takashi Kokubun).


https://github.com/ruby/ruby/pull/2583 was an attempt to reduce method cache misses on Discourse, and IIRC https://github.com/ruby/ruby/pull/2888 removed it. It might be related at least for some extent.

----------------------------------------
Bug #17373: Ruby 3.0 is slower at Discourse bench than Ruby 2.7
https://bugs.ruby-lang.org/issues/17373#change-88989

* Author: sam.saffron (Sam Saffron)
* Status: Open
* Priority: Normal
* ruby -v: 3.0
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
We have a continuous effort to keep https://rubybench.org/ up to date. Unfortunately we have lapsed a bit on updates so I decided to run Discourse bench by hand.

On my local system I am noticing the timing are much slower on Discourse bench than they were on Ruby 2.7: 

```
98c9120cc00ba691b4abcc13a49a30fa54638535

---
categories:
  50: 34
  75: 35
  90: 36
  99: 40
home:
  50: 47
  75: 50
  90: 56
  99: 92
topic:
  50: 53
  75: 55
  90: 58
  99: 92
categories_admin:
  50: 33
  75: 34
  90: 38
  99: 68
home_admin:
  50: 45
  75: 47
  90: 51
  99: 95
topic_admin:
  50: 51
  75: 52
  90: 54
  99: 59
timings:
  load_rails: 1449
ruby-version: 3.0.0-p-1
rss_kb: 293808
pss_kb: 284244

2.7.2


---
categories:
  50: 29
  75: 30
  90: 33
  99: 43
home:
  50: 42
  75: 43
  90: 47
  99: 73
topic:
  50: 47
  75: 47
  90: 52
  99: 54
categories_admin:
  50: 30
  75: 31
  90: 36
  99: 56
home_admin:
  50: 41
  75: 43
  90: 48
  99: 71
topic_admin:
  50: 47
  75: 48
  90: 52
  99: 55
timings:
  load_rails: 1339
ruby-version: 2.7.2-p137
rss_kb: 296836
pss_kb: 287310


2.6.6


---
categories:
  50: 30
  75: 30
  90: 31
  99: 51
home:
  50: 40
  75: 42
  90: 60
  99: 79
topic:
  50: 47
  75: 48
  90: 53
  99: 71
categories_admin:
  50: 30
  75: 31
  90: 35
  99: 50
home_admin:
  50: 41
  75: 43
  90: 62
  99: 100
topic_admin:
  50: 48
  75: 49
  90: 65
  99: 93
timings:
  load_rails: 1464
ruby-version: 2.6.6-p146
rss_kb: 332268
pss_kb: 322865
```

Concretely this means a typical "homepage" view is taking 47 milliseconds now, when in the past it was taking 42 or even 40 ms.

There may be some issues with the bench, you can see it here: 

https://github.com/discourse/discourse/tree/ruby-3

The script to run the bench is `ruby script/bench.rb`

I re-tested against a cleanly built Ruby 2.7 direct from the Git branch to ensure compilation was not at fault.


This is pretty concerning, Discourse bench usually tracks Rails performance pretty accurately. 

---Files--------------------------------
aaron ��� perf _home_aaron_git_railsbench ��� ssh whiteclaw.local ��� 175��54 2020-12-07 12-41-12.png (842 KB)
aaron ��� perf _home_aaron_git_railsbench ��� ssh whiteclaw.local ��� 175��54 2020-12-07 12-41-58.png (874 KB)
aaron ��� perf _home_aaron_git_railsbench ��� ssh whiteclaw.local ��� 299��65 2020-12-07 13-19-20.png (142 KB)


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