Slow layout performance in hello_rust

[steveklabnik]

Sorry for the terrible title, I'm not sure what a good one is here.

Basically, https://steveklabnik.github.io/hello_rust/ loaded in firefox works pretty awesome. the same page loaded in servo (after applying #3585 ) is very, very, very slow. With only a few slides, it's fast, but it gets slower the more you add. It feels O(n^2) but i haven't done any formal benchmarking.

It also happens when you build with --release.

[jdm]

Profiling under instruments shows me that more than 70% of time is spent in layout workers.

cc @pcwalton

[kmcallister]

Interesting. I have a 34-slide deck and performance is adequate in a release build Servo on Linux. I'm building 0e95d6d which was the head of @jdm's PR last I fetched it.

[kmcallister]

Perf on https://steveklabnik.github.io/hello_rust/ is also fine in my build.

[pcwalton]

We have incremental reflow now as well as several font-related bugs fixed so that might have fixes it.

[kmcallister]

But I'm on this old PR branch, I didn't rebase recently...

[nox]

That doesn't seem to be true anymore.