1618968 - First frame rendering takes longer in Fenix than Fennec due to WebRender

Status: RESOLVED WONTFIX

(Core :: Graphics: WebRender, defect, P3)

Description

[Sean Feng [:sefeng]]

Fennec: https://perfht.ml/2Tn79w5
Fenix: https://perfht.ml/2vg3ick

There profiles were taken on Pixel 3.

Based on these 2 profiles, there was a 470ms gap between the www.google.com request is finished to the first paint, and it was only 30ms in Fennec. Looks like the delay was due the first composite took 420ms in Fenix.

Comment 1

[Jamie Nicol [:jnicol]]

Hi Sean, would it be possible to include the renderer thread in the Fenix profile?

Comment 2

[Sean Feng [:sefeng]]

Hi Jamie,

Try https://perfht.ml/2VGm47n, would you be able to see it this time?

The renderer thread was included, but you need to click that " 6/7 tracks visible" button to make it visible.

Comment 3

[Jamie Nicol [:jnicol]]

Oh sorry! Silly me, I always forget about that!

Looks like all the time is spent compiling shaders, which is sort of expected on first launch. Is this taking place on a fresh profile? Does a subsequent app launch exhibit the same behaviour, or is it faster?

Comment 4

[Sean Feng [:sefeng]]

It was a fresh install and the first launch.

Seems like subsequent app launch doesn't exhibit the same behaviour, much faster. This is the profile from a subsequent app launch https://perfht.ml/38qdKeu. Around 100ms this time.

Comment 5

[Jamie Nicol [:jnicol]]

optimized shaders mitigated this, but it's still an unavoidable downside of webrender vs layers. but there's not much point comparing to layers nowadays. we should instead get more recent startup profiles and see what can be improved