[webkit-dev] optimizing browser handling of Facebook Timeline scrolling

Maciej Stachowiak mjs at apple.com
Tue Feb 14 11:06:15 PST 2012

On Feb 14, 2012, at 10:25 AM, Steven Young wrote:

>>>> (2) 50% of time spent painting images... This is a simple speed vs quality tradeoff. If you down-sampled the images on the server, they'd download and paint much faster.
> Thanks. Downsampling sounds like a straightforward solution. We can
> show the higher quality image if they open the photo.

The significant time spent painting images could simply be a sign that too much of the page is being repainted when scrolling, which could be a side effect of unnecessary re-layouts. So this could just another symptom of the "layout thrash" problem. Thus, I would suggest fixing the other issues and retesting before you move to downsample images.

> Btw, what tool are you using that tells you what item is being
> repainted when the cpu is pegged?

I would guess that Geoff is using the Instruments tool on Mac OS X, but it likely takes some expert knowledge to interpret the profile. You can tell by looking at the profile what kind of things are getting painted, but not necessarily the specific item.


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