735895 - nsCSSRendering::PaintBackground takes too long

Status: NEW

(Core :: Web Painting, defect)

Description

[Jeff Muizelaar [:jrmuizel]]

We spend a large chunk (46%) of our painting time on CNN drawing backgrounds. We should try to do something cheaper

Comment 1

[Mark Finkle (:mfinkle) (use needinfo?)]

Waiting for Ali to get back to us with details before making a blocking decision.

Comment 2

[Ali Juma [:ajuma]]

While loading CNN on a Galaxy Nexus, we spend around 700 ms in nsCSSRendering::PaintBackground. Most individual calls are fast (the average call takes about 0.4 ms), but we make a *lot* of calls (around 1700), and a handful of these calls (around 10) do take a significant amount of time (between 10 and 25 ms).

Of the time we spend in nsCSSRendering::PaintBackground, about 67% is in gfxUtils::DrawPixelSnapped.

And of the time we spend in gfxUtils::DrawPixelSnapped, about 30% is in CreateSamplingRestrictedDrawable (however, on other pages, this is 10-15%), and the rest is in the call to gfxDrawable::Draw.

Comment 3

[Jeff Muizelaar [:jrmuizel]]

(In reply to Ali Juma [:ajuma] from comment #2)
> While loading CNN on a Galaxy Nexus, we spend around 700 ms in
> nsCSSRendering::PaintBackground. Most individual calls are fast (the average
> call takes about 0.4 ms), but we make a *lot* of calls (around 1700), and a
> handful of these calls (around 10) do take a significant amount of time
> (between 10 and 25 ms).
> 
> Of the time we spend in nsCSSRendering::PaintBackground, about 67% is in
> gfxUtils::DrawPixelSnapped.
> 
> And of the time we spend in gfxUtils::DrawPixelSnapped, about 30% is in
> CreateSamplingRestrictedDrawable (however, on other pages, this is 10-15%),
> and the rest is in the call to gfxDrawable::Draw.

The question we need to answer is: is the work we're doing necessary and why. i.e. do the times we see match what we would expect them to be.

Comment 4

[JP Rosevear [:jpr]]

What are the costs on planet.mozilla.org and nytimes.com?

Comment 5

[Ali Juma [:ajuma]]

(In reply to JP Rosevear [:jpr] from comment #4)
> What are the costs on planet.mozilla.org and nytimes.com?

On planet.mozilla.org, we spend around 185 ms in PaintBackground. The average call takes about 1.85 ms, but as on cnn.com, there are a handful of calls that take a significant amount of time (between 10 and 35 ms). Of the time we spend in PaintBackground, about 85% is in DrawPixelSnapped. And of the time we spend in DrawPixelSnapped, about 30% is in CreateSamplingRestrictedDrawable.

On nytimes.com, we spend around 245 ms in PaintBackground. The average call takes about 0.5 ms, and no call takes more than 2.5 ms. Of the time we spend in PaintBackground, about 75% is in DrawPixelSnapped. And of the time we spend in DrawPixelSnapped, about 20% is in CreateSamplingRestrictedDrawable.

Comment 6

[JP Rosevear [:jpr]]

If we have any more specific bugs besides bug 733941, please nom those individually.