[wp-trac] [WordPress Trac] #57687: Add automated performance testing CI workflow MVP

[WordPress Trac]

#57687: Add automated performance testing CI workflow MVP
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 Reporter:  adamsilverstein   |       Owner:  mukesh27
     Type:  enhancement       |      Status:  assigned
 Priority:  normal            |   Milestone:  6.3
Component:  Build/Test Tools  |     Version:  trunk
 Severity:  normal            |  Resolution:
 Keywords:  needs-patch       |     Focuses:  performance
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Comment (by oandregal):

 Another thought about meaningful things to track. In addition to: "server
 time" (TTFB) and "user time" (LCP), **there is value for us to understand
 the time it takes the client to render the data it receives**.

 In https://github.com/WordPress/gutenberg/pull/48288 I'm proposing to add
 a new metric to Gutenberg's front-end performance suite: LCP-TTFB. I'm
 unaware of any industry metric that tracks the same thing, I'll be happy
 to adapt if there's any. The rationale is that TTFB takes so much of the
 LCP (50% for classic themes and 80% for block themes) that it may hide any
 meaningful difference in the client-side rendering. For example, changes
 that add blocking scripts/styles that impact LCP negatively may be hidden
 if we improve TTFB in big ways when comparing WordPress releases.

 As a matter of fact, take a look at the
 [https://docs.google.com/spreadsheets/d/1LroIJoYz-
 O9CpfJzaiKYYMWJ7GbE5RZoW1rf1R4FqyA/edit#gid=996638482 latest numbers by
 Felix] that include LCP:

 ||= Metric =||= WP 6.2 beta2 =||
 || LCP-TTFB for TT3 || 103,1ms ||
 || LCP-TTFB for TT1 || 131.85ms ||

 According to this data, block themes are 1,25 faster than classic themes
 when it comes to client side rendering.

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Ticket URL: <https://core.trac.wordpress.org/ticket/57687#comment:4>
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