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Bug 229146 - Firefox causes X to uses 50%+ CPU while waiting for page to load
Summary: Firefox causes X to uses 50%+ CPU while waiting for page to load
Alias: None
Product: Fedora
Classification: Fedora
Component: firefox
Version: 6
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Gecko Maintainer
QA Contact:
Depends On:
TreeView+ depends on / blocked
Reported: 2007-02-18 16:38 UTC by Jon Burgess
Modified: 2018-04-11 14:51 UTC (History)
4 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Last Closed: 2007-03-08 16:51:29 UTC

Attachments (Terms of Use)

System ID Priority Status Summary Last Updated
Mozilla Foundation 372306 None None None Never

Description Jon Burgess 2007-02-18 16:38:51 UTC
Description of problem:
I've noticed that when firefox waits for a page to load the X server often takes
50%+ CPU. After trying a lot of combinations I think i've finally narrowed this
down to a problem with the tabbed window support.

Version-Release number of selected component (if applicable):
also occurs with ff- i686 linux download

How reproducible:
Every time i'm waiting for a page to load with 2+ tabs open.

Steps to Reproduce:
1. Launch firefox -ProfileManager
2. create new profile with default options and launch.
3. try accessing a page which does not exist. For me is a good
one. This causes the browser to try loading the page for ~30 seconds until timeout.
4. While firefox is still trying to load the page, open an xterm run top. Look
at X cpu usage. 
5. After a few seconds of activity X will show ~1% CPU usage (i.e. everything
looks normal now).
6. Stop page load in firefox.
7. Go into preferences->tabs. Enable the "show tabs even when only one window
open" option so that the tab bar appears.
8. Try going to again.
9. Watch X CPU usage. For me X jumps to 50%+ and stays there for the 30+ seconds
that firefox tries to load the page
Actual results:
Having the tab bar open seems to cause firefox to hammer the X server while
loading new pages. At a guess, it could be the updates to do the nice
'Loading...' animation of the tabbed window title bar which cause the problem.

Expected results:
This is running FF on an AMD64 3000 so I don't expect the X server to need 50%+
CPU in order to tell me that FF is waiting for a page to load.

Additional info:
I'm using an NVidia FX5200 with the open source 'nv' driver. 
I tried disabling pango with no effect.
The high X CPU still occurs even with firefox minimised so I don't think it is
due to the X driver code trying to repaint the screen.

I guess this is really an upstream issue since I see the same with the i686 binary release. Let me know if you want me to open a
bug at

Comment 1 Matěj Cepl 2007-02-27 20:51:03 UTC
Yes, please, and let us know the number of the new bug (it would be nice of you
to search first to find out whether there isn't duplicate
bug of the same issue).

Comment 2 Jon Burgess 2007-03-01 21:45:26 UTC
I see the same with the trunk mozilla 3.0a3pre. Did a quick search in
for CPU and tabbed browsing and while there are lots of high firefox CPU bugs
reported none seem to be specific to X CPU and loading tabbed pages. Raised a
new bug

Comment 3 Matěj Cepl 2007-03-08 16:51:29 UTC
OK, so I am closing this as an upstream bug. Thanks for the info.

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