https://www.w3.org/conf/2013sf/ uses too much GPU time

[mstange]

With the integrated GPU on my Macbook Pro, https://www.w3.org/conf/2013sf/ uses about 12ms of GPU time. I exported a frame as a YAML + resources zip: http://tests.themasta.com/w3.zip

Here's a screenshot of the webrender profiler on cargo run --release -- -p 1 show w3/w3.yaml:

[glennw]

There are a lot of clips and blurs occurring in that profile - we'll need to investigate why (or why they are slow).

This is also (probably) a good example of how in the Gecko integration we're not currently getting any z-buffer benefits - most pixels on here are opaque, so we'll probably benefit a lot from early z-reject once this is fixed in WR.

[mstange]

Adjusting the text shadow blur radius to match Gecko might also improve this slightly.

[mstange]

The inner rect workaround from #1820 regressed this testcase by about 50%: The GPU time on my machine with the integrated GPU went from 10.91ms to 16.11ms.

[kvark]

Thanks @mstange . Time to revisit my proposal of #1828 to address this properly?

[mstange]

The shadow changes increased this to 340ms.

[mstange]

With the blur optimizations from #1896, it goes down to 60ms.

[glennw]

Wow! I'll take a look at this today, and write up any findings here.

[metajack]

cc @metajack

[glennw]

I logged out all the blur render tasks that are added for this test case:

new_blur r=24 t=Alpha s=1756×13711
new_blur r=4 t=Color s=810×74
new_blur r=4 t=Color s=865×74
new_blur r=4 t=Color s=602×74
new_blur r=4 t=Color s=280×74
new_blur r=4 t=Color s=224×74
new_blur r=4 t=Color s=198×74
new_blur r=4 t=Color s=207×74
new_blur r=4 t=Color s=255×74
new_blur r=4 t=Color s=216×74
new_blur r=4 t=Color s=219×74
new_blur r=4 t=Color s=222×74
new_blur r=4 t=Color s=255×74
new_blur r=4 t=Color s=338×74
new_blur r=4 t=Color s=314×74
new_blur r=4 t=Color s=224×74
new_blur r=4 t=Color s=234×74
new_blur r=4 t=Color s=230×74
new_blur r=4 t=Color s=274×74
new_blur r=4 t=Color s=227×74
new_blur r=4 t=Color s=219×74
new_blur r=4 t=Color s=272×74
new_blur r=4 t=Color s=761×168
new_blur r=6 t=Alpha s=946×120
new_blur r=4 t=Color s=161×74
new_blur r=4 t=Color s=108×74
new_blur r=4 t=Color s=157×74
new_blur r=4 t=Color s=148×74
new_blur r=4 t=Color s=122×74

Wow, I think new_blur r=24 t=Alpha s=1756×13711 might be the problem (and a bug)!!

Investigating now... :)

[glennw]

Perhaps the more surprising thing is that it manages to do a blur with a radius of 24 at that resolution in "only" 60 ms...!

[glennw]

Which due to the way passes allocate an array texture results in allocating 3x 2048x13711 alpha targets, which is 84 MB of alpha frame buffer to clear, in addition to the blurs...

[glennw]

Ah, this page has a huge box shadow applied to the entire body element, which is very long due to scrolling. WR is not clipping this to the visible screen when rendering an off-screen target. I'll work on a fix for this today, which should have a massive improvement in GPU time for this test case.