[ruby-core:101904] [Ruby master Bug#17373] Ruby 3.0 is slower at Discourse bench than Ruby 2.7

Issue #17373 has been updated by sam.saffron (Sam Saffron).


Good news, @ko1 and @tenderlove managed to recover a fair bit of performance leading to release. 

3.0 remains slower in our bench than 2.7 but we did improve over the first post. 

Koichi san believes that some of the performance is now lost cause mc_inline_miss_same_cme is no longer cached in 3.0.

That said, the picture as of release is: 

Ruby 2.6 -> Ruby 2.7 -> Ruby 3.0 

categories page / median:  26 -> 27 -> 28 (slow down 1ms from 2.7 ... 2ms from 2.6) 
home page: 50 -> 51 -> 53 
topic page: 44 -> 46 -> 49
cat admin: 26 -> 27 -> 28
home admin: 50 -> 53 -> 53
topic admin: 44 -> 45 -> 48 

Interestingly when I test this all from the same process some of this slowdown is no longer observed, so some of the slowdown could be due to IO changes or GC.


 


----------------------------------------
Bug #17373: Ruby 3.0 is slower at Discourse bench than Ruby 2.7
https://bugs.ruby-lang.org/issues/17373#change-89747

* 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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