1643802 - raptor-tp6-imgur-firefox load time is slower with Fission than non-Fission (200% on Linux and 20% on Windows)

Status: RESOLVED WONTFIX

(Core :: DOM: Content Processes, defect, P2)

Description

[Chris Peterson [:cpeterson]]

Attachment: Screenshot_2020-06-05 Treeherder.png

Link to Perfherder results:

https://treeherder.mozilla.org/perf.html#/graphs?highlightAlerts=1&series=mozilla-central,1978301,1,10&series=mozilla-central,2237551,1,10&series=mozilla-central,1936087,1,10&series=mozilla-central,2237580,1,10&timerange=2592000

Why is Linux so much slower than Windows?

Did Jesup's preallocation process changes around May 31 cause Linux load time to get even worse?

See the attached Perfherder screenshot for posterity.

Comment 1

[Tarek Ziadé (:tarek)]

ccing Jesup

Comment 2

[Randell Jesup [:jesup] (needinfo me)]

Imgur is very sensitive to timing during load; loads on a windows and linux (both with fission) have a 2x difference in loadtime, with minimal difference in visual metrics (eyeballed). The difference appears to be whether the 2nd group of loads gets started before load fires (and so they all block load). On one (linux) load happened a few ms after first-contentful-paint (with very little of the page visible, and only the first group of images/anims). On the other, load happened at the very end when all images/anims are loaded and visible.

I'm going to continue to investigate overall load time. I see indications in the perfherder results of this 2x factor showing up, sometimes noisily in the results (fission and non-fission, though on linux fission may be pushing it mostly over the line and triggering 2x loadtimes frequently/often).

I suspect that visual metrics won't show much if any differences, at least not the 2x kind.

We do still seem to have a delta in performance on windows, though, so we are slower with fission.

Note that the tests seem to have been disabled June 23.

Comment 3

[Neha Kochar [:neha]]

We'll monitor visual metrics and not pageload so closing this. We'll file separate bugs for visual metrics Fission regressions.