Bug 260446 – [GTK] Rendering is broken with Lower Power Mode

• Component: WebKitGTK
• Status: RESOLVED DUPLICATE

[Abrar Ahmed]

Created attachment 467347 [details]
Recording of page content not being updated until resize

Trying to scroll a webpage with Low Power Mode (enabled via setting the system power profile to 'Power Saver') is broken. The scrolling works and the web elements are being moved but the changes are not animated/shown. Forcing a relayout by changing the webview size will update and show the correct content. Animations in general seem broken on all pages.

[Abrar Ahmed]

I forgot to mention the fact that I'm running Epiphany Tech Preview. Epiphany 44 doesn't seem to have this problem (no low power mode?).

[Abrar Ahmed]

I've noticed now that this problem also occurs sometimes when I'm using the 'Balanced' profile too. It doesn't occur in a perfectly reproducible manner unlike with the 'Power Saver' mode.

[Michael Catanzaro]

(In reply to Abrar Ahmed from comment #1)
> I forgot to mention the fact that I'm running Epiphany Tech Preview.
> Epiphany 44 doesn't seem to have this problem (no low power mode?).

Low power mode has been around for years.

[Abrar Ahmed]

(In reply to Michael Catanzaro from comment #3)
> (In reply to Abrar Ahmed from comment #1)
> > I forgot to mention the fact that I'm running Epiphany Tech Preview.
> > Epiphany 44 doesn't seem to have this problem (no low power mode?).
> 
> Low power mode has been around for years.

I did not know that. I can still reproduce the issue with WEBKIT_DISABLE_DMABUF_RENDERER=1 set as well. 
https://bugs.webkit.org/show_bug.cgi?id=260073 seems like I just found a case where this issue pops up more consistently? I'm observing the same sort of behaviour.

[Michael Catanzaro]

Bug #260073 is definitely not related to low power mode, because I have a desktop computer. :)

[Michael Catanzaro]

*** Bug 261434 has been marked as a duplicate of this bug. ***

[Michael Catanzaro]

Anyway, I can reproduce by manually enabling low power mode. It immediately breaks rendering, and the effect is permanent: disabling low power mode does not fix it, only a cross-site navigation to trigger a process swap seems sufficient to get the web view to work again.

It's not just a problem with animations or scrolling. For example, selecting text in the text entries on this Bugzilla does not work. However, I can load new pages and they initially render just fine. But all subsequent rendering is broken.

It seems LowPowerModeNotifier is only used by Page::handleLowModePowerChange (which is a typo, should be Page::handleLowPowerModeChange), so whatever is going wrong must be caused by that. Most notably, it sets a throttling reason ThrottlingReason::LowPowerMode and calls RenderingUpdateScheduler::adjustRenderingUpdateFrequency.

[Michael Catanzaro]

(In reply to Abrar Ahmed from comment #2)
> I've noticed now that this problem also occurs sometimes when I'm using the
> 'Balanced' profile too. It doesn't occur in a perfectly reproducible manner
> unlike with the 'Power Saver' mode.

The non-reproducible variant of this is bug #260073. Carlos Garcia has fixed two different reproducible cases thus far, and this bug smells like a third. Unfortunately low power mode is definitely not the only way to trigger it.

[Michael Catanzaro]

I'm going to bisect this even if we don't actually need to do so to debug the issue, because I suspect the bisect result might be relevant to that bug #260073.

[Carlos Garcia Campos]

*** This bug has been marked as a duplicate of bug 260073 ***