Bug 126970 – [ATK] AXChildrenChanged notification handling is a performance black hole

• Status: RESOLVED
• Resolution: FIXED
• Component: WebKitGTK

[Zan Dobersek]

in AXObjectCache::postPlatformNotification, handling the AXChildrenChanged is causing great performace reduction when loading the single-page HTML Living Standard document.
http://trac.webkit.org/browser/trunk/Source/WebCore/accessibility/atk/AXObjectCacheAtk.cpp#L196
http://www.whatwg.org/specs/web-apps/current-work/

[Zan Dobersek]

Commenting out that code block reduces the time of load from 60 seconds down to 15 seconds.

The ref-deref cycle is fired more than a million times during the load, and AccessibilityObject::updateBackingStore() is called twice per cycle, causing additional work that hinders the performance.

[Mario Sanchez Prada]

Created attachment 221130 [details]
Patch proposal

This should be enough to fix this issue. Sorry for the issue in the first place (and thanks Zan for reporting it)

[Gustavo Noronha (kov)]

Comment on attachment 221130 [details]
Patch proposal

View in context: https://bugs.webkit.org/attachment.cgi?id=221130&action=review

> LayoutTests/accessibility/children-changed-sends-notification-expected.txt:12
> -PARAGRAPH notification: AXChildrenAdded
> -GLOBAL notification: AXChildrenAdded on element with role AXRole: AXParagraph
>  PARAGRAPH notification: AXChildrenRemoved
>  GLOBAL notification: AXChildrenRemoved on element with role AXRole: AXParagraph
> +PARAGRAPH notification: AXChildrenAdded
> +GLOBAL notification: AXChildrenAdded on element with role AXRole: AXParagraph

Does this not affect Mac? Is this test specific for ATK?

[Mario Sanchez Prada]

Comment on attachment 221130 [details]
Patch proposal

(In reply to comment #3)
> (From update of attachment 221130 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=221130&action=review
> 
> > LayoutTests/accessibility/children-changed-sends-notification-expected.txt:12
> > -PARAGRAPH notification: AXChildrenAdded
> > -GLOBAL notification: AXChildrenAdded on element with role AXRole: AXParagraph
> >  PARAGRAPH notification: AXChildrenRemoved
> >  GLOBAL notification: AXChildrenRemoved on element with role AXRole: AXParagraph
> > +PARAGRAPH notification: AXChildrenAdded
> > +GLOBAL notification: AXChildrenAdded on element with role AXRole: AXParagraph
> 
> Does this not affect Mac? Is this test specific for ATK?

The mac is currently skipping this test, so yes, this test is specific to ATK.

Thanks for the review!

[WebKit Commit Bot]

Comment on attachment 221130 [details]
Patch proposal

Clearing flags on attachment: 221130

Committed r161966: <http://trac.webkit.org/changeset/161966>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.