[wp-trac] [WordPress Trac] #57648: Major performance regression in `wp_enqueue_global_styles()` for classic themes

[WordPress Trac]

#57648: Major performance regression in `wp_enqueue_global_styles()` for classic
themes
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 Reporter:  flixos90      |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  6.2
Component:  Editor        |    Version:
 Severity:  major         |   Keywords:
  Focuses:  performance   |
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 I just finished conducting a quick performance analysis for WordPress 6.2,
 which I did in preparation for Beta tomorrow, to see how things are
 looking performance-wise. The objective of the analysis was to measure
 Server Timing metrics in latest 6.2 `trunk` and compare them to the same
 metrics in the 6.1 branch.

 While overall things were looking good, there was one ''major'' regression
 in template execution time for the classic theme tested (Twenty Twenty-
 One). After digging in a bit further, it became clear that this regression
 is caused by some logic triggered in `wp_enqueue_global_styles()`, with
 that function now taking 5 times longer than in WP 6.1.

 Investigating the root cause for this regression and fixing it is
 critical, as it also means a significant regression of ~30% for
 WordPress's ''overall'' load time for classic themes.

 Here is a spreadsheet with the test results from my analysis:
 https://docs.google.com/spreadsheets/d/1p8Bw8Y_53NlZ8rHRmXn-
 a_fJj3XBe8Ajf6w9eCHKecI/edit
 All numbers in there are based on median values from 20 requests each, to
 account for any variance. It is safe to say that this is a real regression
 and not caused by variance between requests.

 All other measurements look very solid, with improvements in comparison to
 6.1, so we need to address this regression in order to ensure 6.2 is a win
 for performance.

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Ticket URL: <https://core.trac.wordpress.org/ticket/57648>
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