1501415 - 5+ second delay before first paint, when loading 27mb plaintext log file

Status: NEW

(Core :: Layout: Text and Fonts, defect, P3)

Description

[Daniel Holbert [:dholbert]]

STR:
 1. Load this file:
https://taskcluster-artifacts.net/XZmhivqwQUKrk15pEu7R9Q/0/public/logs/live_backing.log

(Or if that link dies, download and gunzip attachment 9018049 [details] which is gzipp'ed text version of that ^^ file, and open the resulting text file in Firefox.)


ACTUAL RESULTS:
The first paint takes quite a while -- there's a ~5 second or longer delay before we paint anything.

EXPECTED RESULTS:
Something should be painted sooner.


Note for comparison: Chrome seems to take as long or longer as we do, to *finish loading the file* (same goes for gedit, the Ubuntu text editor).  However, we take much longer to get to our first nonblank paint.

Spinning this off from bug 515447. Calling this [qf:p3] per QF triage today.

Comment 1

[Daniel Holbert [:dholbert]]

For the record, here's a profile of me loading that taskcluster URL: https://perfht.ml/2AoL2gt

Comment 2

[Boris Zbarsky [:bzbarsky]]

Unsurprisingly, all the non-poll() time in the profile is under one of gfxFontGroup::MakeTextRun, BuildTextRunsScanner::SetupBreakSinksForTextRun, gfxTextRun::BreakAndMeasureText.

It's worth seeing how much data the parser dumps into the DOM before it yields to layout for the first time.