706250 - Many short unresponsive periods when loading The Daily What

Status: NEW

(Core :: DOM: Core & HTML, defect, P5)

Description

[Mark Côté [:mcote]]

Attachment: Simple peptest demonstrating unresponsiveness while loading page

The Daily What is a blog with lots of images, videos, and ads from various sources.  It always felt a bit slow to load for me, so I made a very simple peptest, which confirms that there are many periods where the unresponsiveness goes above 50 ms while the page is loading:

PEP TEST-START | test_dailyWhat.js
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 103 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 199 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 112 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 204 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 105 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 57 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 79 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 194 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 202 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 68 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 182 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 63 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 84 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 118 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 51 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 55 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 67 ms
PEP WARNING    | test_dailyWhat.js | open_page | unresponsive time: 215 ms
PEP TEST-UNEXPECTED-FAIL | test_dailyWhat.js | fail threshold: 0.0 | metric: 322.362
PEP TEST-END   | test_dailyWhat.js | finished in: 9426 ms

This was on 64-bit Ubuntu 11.10 on a MacBook Pro.  I have confirmed that this also occurs in 32-bit Firefox on a 64-bit Windows 7 machine (one unresponsive period was over 3 seconds in length).

Attached is the peptest that simply loads the page and looks for unresponsiveness.  To run the test, see https://wiki.mozilla.org/Auto-tools/Projects/peptest#Running_Tests.

Comment 1

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

What does "unresponsive time: N ms" mean in this context?  That we went N ms without servicing the event loop?

Comment 2

[Mark Côté [:mcote]]

Yup, that's what it means.  It uses ted's EventTracer code: http://blog.mozilla.com/ted/2011/06/27/measuring-ui-responsiveness/

Peptest specifically notes when the event loop was stuck for more than 50 ms during particular actions, as per the requirements of Project Snappy.

Comment 3

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

Ok, the next question here then is what we're doing during those intervals.  Can this tool tell us that, or do we need to dig in with other tools?

Comment 4

[Andrew Halberstadt [:ahal]]

Not yet, I think we'll be able to use the work done on bug 580055 but it is currently blocked.

Comment 5

[Andrew McCreight [:mccr8]]

This could be a good testcase, but it sounds like we'd need somebody to run a profiler, or wait until we have better profiling tools, to analyze what is going on here.

Comment 6

[Firefox Bug Husbandry Bot]

https://bugzilla.mozilla.org/show_bug.cgi?id=1472046

Move all DOM bugs that haven’t been updated in more than 3 years and has no one currently assigned to P5.

If you have questions, please contact :mdaly.