[tbb-bugs] #19276 [Applications/Tor Browser]: Scrolling is slow and CPU intensive

[Tor Bug Tracker & Wiki]

#19276: Scrolling is slow and CPU intensive
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 Reporter:  cypherpunks                          |          Owner:  tbb-
     Type:  defect                               |  team
 Priority:  Medium                               |         Status:
Component:  Applications/Tor Browser             |  needs_information
 Severity:  Normal                               |      Milestone:
 Keywords:  tbb-6.0-issues, tbb-usability, tbb-  |        Version:
  performance                                    |     Resolution:
Parent ID:                                       |  Actual Points:
 Reviewer:                                       |         Points:
                                                 |        Sponsor:
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Comment (by 49ax56xr36):

 Replying to [comment:15 yawning]:
 > Try setting `layers.offmainthreadcomposition.enabled` to `false`.
 Behavior is noticeably different on my Poulsbo Atom box (using the open
 source 2D only drivers).

 The default for this setting in 6.0.1 is =false and that's what has been
 in effect.  Set it to =true and it works better both with xrender=false
 and xrender=true.  Seems a proper result as the event loop is presumably
 separated from rendering and can respond to mouse and keyboard events even
 while the browser is bogged down rendering.

 I'm keeping 'offmainthreadcomposition' active and leaving 'xrender'
 disabled.

 Disabling 'xrender' by default is potentially a diffcult choice--have no
 position on it.  But considering that worst-case beahavior with
 xrender=true is terrible and worst-case with xrender=false is not-bad it
 might be a good idea.

 Or maybe see if there's a "dumb bug" in there that can be fixed.  Making
 the same calls multiple times or in a non-optimal order come to mind.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19276#comment:16>
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