1183163 - Investigate CSS flex performance issues compared to XUL flexbox

Status: NEW

(Core :: Layout, defect)

Description

[Boris Zbarsky [:bzbarsky]]

Neil Deakin has a blog post at https://enndeakin.wordpress.com/2015/07/13/comparing-flexible-box-layouts/ with some charts, but no links to testcases.  Getting those testcases attached here would be useful.

Comment 1

[Daniel Holbert [:dholbert]]

Neil, if you have a patch-stack that CSS-flexifies a mozilla-central build (and reproduces the issues documented in your blog post), I'd love to work with that patch-stack locally & see what I can find.

Comment 2

[Daniel Holbert [:dholbert]]

(In reply to Daniel Holbert [:dholbert] from comment #1)
> Neil, if you have a patch-stack that CSS-flexifies a mozilla-central build

Ah, turns out this was simpler than I expected; I just tried adding a line to the end of browser.css, per the end of https://enndeakin.wordpress.com/ , and was able to trigger some pathological slowness.

Comment 3

[Daniel Holbert [:dholbert]]

Attachment: demo-patch #1: make everything display:flex, in browser.css [SLOW]

This patch triggers the pathological case discussed at the end of Neil's blogpost -- it makes startup take ages (I waited several minutes with 100% CPU and still hadn't seen a window yet).

Comment 4

[Daniel Holbert [:dholbert]]

Attachment: demo-patch #2: make everything display:-moz-box, in browser.css

For comparison, here's a patch to make everything -moz-box instead of flex. With this, startup is pretty quick.