859407 - Scrolling becomes janky quickly due to heavy DOM

Status: RESOLVED FIXED

(DevTools :: Netmonitor, defect)

Description

[Girish Sharma [:Optimizer]]

Attachment: DOM for one network call

Attached image shows one row's DOM.
On an average page, around 20's of these rows will be there (even more on most pages). Adding all the repaints and reflows due to shifting timeline on top of it makes scrolling very slow and laggy/janky. Scrolling is slow even when the timeline is not shifting, i.e. page has completely loaded.

Maybe the DOM can be reduced (as the side arrow is not shown anyways) per row.

My system is pretty fast, so its not system's fault :

CPU : Core i7 3rd gen 3610QM (quad core with hyper threading), 8 GB RAM
GPU : Intel(R) HD Graphics 4000, (GPU #2) NVIDIA GeForce GT 650M
OS : Windows 7, HWA enabled.

Comment 1

[Victor Porof [:vporof][:vp]]

This is a dupe of more bugs. I'm marking bug 859062 here because it's what you suggest with the side arrow.

Slowness happens because of the repeating background in .requests-menu-subitem.requests-menu-waterfall, not DOM (having a depth of 3 or 4 boxes is not that much, tbh). That background will switch to something else in bug 859041.

Comment 2

[Girish Sharma [:Optimizer]]

Then please lets close this bug only when the slowness is gone ? because it might happen that bug 859041 introduces even further slow gradients or more DOM.

> This is a dupe of more bugs. I'm marking bug 859062 here because it's what
> you suggest with the side arrow.

I am not suggesting that, although yes, it is unnecessary here and should be removed.
 
> Slowness happens because of the repeating background in
> .requests-menu-subitem.requests-menu-waterfall, not DOM (having a depth of 3
> or 4 boxes is not that much, tbh). That background will switch to something

but 30+ times repetition of 3-4 level nesting might be much.

Comment 3

[Victor Porof [:vporof][:vp]]

(In reply to Girish Sharma [:Optimizer] from comment #2)
> Then please lets close this bug only when the slowness is gone ? because it
> might happen that bug 859041 introduces even further slow gradients or more
> DOM.
> 

Bug 859041 will switch to a canvas-based background...

Comment 4

[Victor Porof [:vporof][:vp]]

Moving into Developer Tools: Netmonitor component. Filter on NETMONITORAMA.

Comment 5

[Victor Porof [:vporof][:vp]]

(In reply to Girish Sharma [:Optimizer] from comment #2)
> 
> but 30+ times repetition of 3-4 level nesting might be much.

Request items are flat now. Is it still slow?

Comment 6

[Girish Sharma [:Optimizer]]

(In reply to Victor Porof [:vp] from comment #5)
> (In reply to Girish Sharma [:Optimizer] from comment #2)
> > 
> > but 30+ times repetition of 3-4 level nesting might be much.
> 
> Request items are flat now. Is it still slow?

Yes, much better now. And I am assuming that this will get better with canvas based background, so closing :) .