981260 - idling viewing a PDF causes 50% CPU usage

Status: NEW

(Core :: Layout, defect)

Description

[Cameron McCormack (:heycam)]

I'm experiencing high CPU usage when viewing certain PDFs.  For me this one exhibits the problem:

  http://dash.harvard.edu/bitstream/handle/1/2031713/Yellow-pages.pdf?sequence=2

Might need to scroll down a couple of pages for it to happen.

I captured a profile during the high CPU usage:

  http://people.mozilla.org/~bgirard/cleopatra/#report=d63df1fe9b9ebeab2f36385e554072573903224f

We're spending 50% of the time idling, the rest of the time painting frames (but not directly in the window, as paint flashing doesn't show up anything).  Don't know whether this is a problem in pdf.js (there's no JS in the profile, at least) or layout, so filing in Core :: Layout to start with.

Comment 1

[Daniel Holbert [:dholbert]]

(In reply to Cameron McCormack (:heycam) from comment #0)
> We're spending 50% of the time idling, the rest of the time painting frames
> (but not directly in the window, as paint flashing doesn't show up
> anything).

FWIW: canvas repaints don't seem to trigger paint flashing for me, at e.g. these demos with continuously-changing canvases:
 http://html5demos.com/canvas
 https://developer.mozilla.org/en-US/demos/detail/the-spiral-of-pi-vivax-solutions/launch

...so it's definitely possible for us to be continuously repainting a canvas without it showing up via paint flashing.

Comment 2

[Timothy Nikkel (:tnikkel)]

It looks like the painting is about one third building display lists, two thirds frame layer builder processing. Almost no actual pushing of pixels. So maybe something is getting marked as invalid over and over, but it doesn't actually result in changed pixels, and we detect that.