Nickolay_Ponomarev Reporter
	Description • 8 years ago

On a new profile, current nightly:
1. Open https://support.mozilla.org/en-US/questions/1111080
2. Scroll to the bottom of the page with Cmd+Down or with the three(?)-finger swipe.
3. Scroll to the top
4. Repeat

With e10s scrolling is much slower.

When taking the profiles below I did this: scroll down, scroll up, wait a second; repeat.

e10s: https://cleopatra.io/#report=fd056b554af26623e0d24467e351a89d799664e5&filter=%5B%7B%22type%22%3A%22RangeSampleFilter%22,%22start%22%3A214795,%22end%22%3A217711%7D,%7B%22type%22%3A%22RangeSampleFilter%22,%22start%22%3A216117,%22end%22%3A216767%7D%5D&selection=0,2662,2663,2664,2665,2359,2666,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,1039,1040,1041,1042,1043,1044,2713,2714,2715,2716,168,169,170,171,183,184,185,186,187,188,189,190,214,215,216,217,218,219,2877,2878,2879,196,197,198,199,2889

no e10s: https://cleopatra.io/#report=f0ac7ed640459a01ac92b87533ab7f23eb1ae32d&filter=%5B%7B%22type%22%3A%22RangeSampleFilter%22,%22start%22%3A15676,%22end%22%3A17733%7D%5D&selection=0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,502,503,504,505,506,507,508,509,510,511,1758,343,344,447,448,449,450,451,453,463,464,465,466,467,468,468,469,470,738,739,740,472,473,474,475

This is likely a duplicate, but I couldn't find a list of known root causes of bad scrolling perf, and a way to confirm that my problem matches a known cause, so I'm filing this anyway.

	Jeff Muizelaar [:jrmuizel]
	Comment 1 • 8 years ago

What do you mean by slow scrolling? Is it jumpy or is there missing content?

I expect this might have to do with the horizontal scrolling. Do you see this problem on other support questions that are not horizontally scrollable?

	Jeff Muizelaar [:jrmuizel]
	Comment 2 • 8 years ago

Is this on a retina screen?

	Nickolay_Ponomarev Reporter
	Comment 3 • 8 years ago

The scrolling is jumpy: you can notice the time it takes to paint the next frame, both visually and in the profile.

This is a retina screen, yes.

> I expect this might have to do with the horizontal scrolling. 
That was a good guess! I removed the wide <p> from the first post (using the Devtools Inspector) and scrolling became as fast as without e10s.

	Botond Ballo [:botond]
	Comment 4 • 8 years ago

Bug 1251638 is another bug where we've seen the presence of a horizontally scrollable element have a negative effect on scrolling performance. It's possible these share a root cause.

	Jim Mathies [:jimm]
	Comment 5 • 8 years ago

kats, apz related?

	Kartikaya Gupta (email:kats@mozilla.staktrace.com)
	Comment 6 • 8 years ago

Yeah this is next on my to-do list.

	Kartikaya Gupta (email:kats@mozilla.staktrace.com)
	Comment 7 • 8 years ago

I've been using bug 1243081 to investigate since I'm assuming they're the same underlying issue, and it's easier for me to reproduce on that URL. From the APZ side I don't think there's much we can do here without making checkerboarding worse. Doing something like implementing bug 1261166 might help.

	Kartikaya Gupta (email:kats@mozilla.staktrace.com)
	Comment 8 • 8 years ago

As with bug 1243081, applying the WIP patch on bug 1261166 makes the transaction times here drop to ~0. I specifically tested scrolling up and down on the provided URL using fn+left/right arrow (equivalent to "home"/"end" scrolling on mac) and compared the transaction times with and without bug 1261166.

	Botond Ballo [:botond]
	Comment 9 • 8 years ago

(In reply to (Back on May31) Kartikaya Gupta (email:kats@mozilla.com) from comment #8)
> As with bug 1243081, applying the WIP patch on bug 1261166 makes the
> transaction times here drop to ~0.

Just to make sure I'm understanding this correctly: the slowness here is specific to Mac?

	Kartikaya Gupta (email:kats@mozilla.staktrace.com)
	Comment 10 • 8 years ago

I believe so.

	Kartikaya Gupta (email:kats@mozilla.staktrace.com)
	Comment 11 • 8 years ago

Unassigning since I'm not doing anything here, it is just waiting on the ClientStorage implementation.

	Kartikaya Gupta (email:kats@mozilla.staktrace.com)
	Comment 12 • 8 years ago

Sounds like the ClientStorage work is still stalled, so this won't get fixed for 49 or 50 most likely.

	Sylvestre Ledru [:Sylvestre]
	Comment 13 • 6 years ago

Moving to p3 because no activity for at least 1 year(s).
See https://github.com/mozilla/bug-handling/blob/master/policy/triage-bugzilla.md#how-do-you-triage for more information