78826 - Performance issues executing JavaScript.

Status: RESOLVED DUPLICATE of bug 21762

(Core :: DOM: Core & HTML, defect, P3)

Description

[Konstantin Riabitsev]

From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux 2.2.16 i686; en-US; rv:0.9+) Gecko/20010503
BuildID:    0.8.1+

Goging to that page with any build 0.8.1+ (not tested with earlier) causes the
browser to freeze for several seconds (22 on my P2-366) before becoming
responsive again. They utilize pretty advanced JS techniques for dropdown menus,
so that is my educated guess for the source of the problem. I might try to
narrow it down, but the file is a bastard of 800 lines. #mozillazine channel
confirms that this occurs on all platforms.

Reproducible: Always
Steps to Reproduce:
1. http://www.cplc.org/


Actual Results:  Browser freezes over.

Expected Results:  Well, in my perfect little world it should do everything
instanteniously. :)

Comment 1

[Konstantin Riabitsev]

Ackk! The URL in description should be http://www.cplc.com/. Not org. It is
correct in the URL field.

Comment 2

[Jason Johnston]

Has anyone seen how IE handles this?  Netscape4.7 and Konqueror are both sniffed
out of the picture so that no menus appear.  It may just be that it's a big
nasty hairy script.

At least the author is being standards-compliant! ;)

Comment 3

[Phil Schwartau]

Confirming with build 2001042704 WinNT.
 
The site takes about 22 seconds to load:
     12 seconds for the basic page to appear
     10 seconds to create the drop-down menu items via JavaScript


[e-mail]:  This site loads in IE the same way as in NN4.7 : 
                  the drop-down menus are not created. Therefore IE,
                  like NN4.7, doesn't have a performance problem on it.

Comment 4

[Phil Schwartau]

Attachment: Reduced HTML testcase with all JavaScript in-line

Comment 5

[Phil Schwartau]

Load the reduced HTML testcase in Mozilla. You will see the top-level menu
rendered right away. But then you see the CPU pegged at 100% for about 10 
seconds as the drop-down menu items are created dynamically via JavaScript -


Many warnings like this appear in the JavaScript Console:

    Warning: test for equality (==) mistyped as assignment (=)?
    Source File: file:///C:/WINNT/Profiles/pschwartau/Desktop/78826_XXX.html
    Line: 1054, Column: 93
    Source Code: if (document.all.formelements[x].style.visibility = "visible") 

Comment 6

[Konstantin Riabitsev]

Fixing the warnings, however, doesn't improve the performance. Also, that is
strictly IE's code, so Mozilla doesn't execute it at all (since condition for
document.all is negative).

Comment 7

[Phil Schwartau]

Attachment: Same testcase, with all JavaScript errors corrected

Comment 8

[Phil Schwartau]

The 2nd testcase takes roughly the same time to load, even with the 
JavaScript errors corrected. I will attach WinNT stack traces I obtained 
by interrupting the page load of the 2nd testcase in a debugger. 

I do not have Quantify, so I can't give a better analysis of exactly
what takes so long -

Comment 9

[Phil Schwartau]

Attachment: WinNT stack traces after interrupting page load of testcase

Comment 10

[Phil Schwartau]

Is this is a browser performance issue or a JS Engine performance issue?
By looking at the stack traces, I'm going to say browser and reassign. 

Sending to DOM. jst will know better whether this is DOM, Layout,
or JS Engine, etc. Please reassign back if this is JS Engine -

Comment 11

[Johnny Stenback (:jst)]

Looks like more of the style resolution perf. problems with dynamic pages. Over
to attinasi.

Comment 12

[Konstantin Riabitsev]

A page with a very similar problem:

http://www.ada.org/public/index.asp

Same stuff -- drop-down menus.

Comment 13

[Fabian Guisset]

Perf doesn't sound bad on my (admittedly speedy) athlon 1ghz with 256MB RAM.
However ther is a little problem: After mousing over a menu item, the popup
appears -- fine. Then I put my mouse on the popup to select a menu item, but the
popup disappears. Am I just missing something?

Comment 14

[James Green]

Yep 20secs or more to start the page here on my P300. BTW,
http://www.ada.org/public/index.asp does not exhibit the slow loading problem
for me.

Comment 15

[Navid]

www.telusmobility.com displays the same type of problems as cplc.com, but the
performance is much worse (takes approx. 10 seconds for the "Products and
Services" menu to appear with CPU utilization at 100%)

Not sure if the source of the problem is the same, but I didn't want to open a
new bug for it.

I'm using build 20010531 on Win2K on a Pentium III 450 Mhz

Comment 16

[Marc Attinasi]

IE 5.5 on the Mac has the same performance problems (and it displays the menus)
- in fact, we are a little bit faster (5 sec on my G4 with Mozilla, 6 sec with IE)!

FWIW: On my Win2K machine I can see no difference in the performance before and
after the recent style rule matching improvements.

I certainly think it is worth investigating the performance problems, but this
is not an rtm stopper so I'm setting the milestone to 1.0. I'll dig in with
Quantify and see what we are doing.

Comment 17

[Fabian Guisset]

marking as dup of bug 21762 as no specific problem is demonstrated in this bug.
Please see my post in npm.dom for more information.

*** This bug has been marked as a duplicate of 21762 ***