Multi-threaded rendering is less of a win when a single desktop core is already pretty powerful. Servo is going to make a big difference on mobile platforms with multiple underpowered cores.
A 3 Ghz P4 from 2005 way well blitz a Core-M from 2015 on certain single-threaded benchmarks. But if you're concerned about energy bills, emissions, fanless computing or all day battery life then performance per watt matters even on x86-64 desktop environments.
From the article:
parallelism results in power savings. Multiple threads working in parallel on a page-rendering job allow the CPU to complete the entire page in the same amount of time while running at a lower frequency.
That's not true. Layout is still often slow (multi-hundred ms) on desktop. You can notice that.
Also powerful x86 CPUs are so good at shared-memory multithreading (cache coherency, large caches) that x86 is actually the best case for us (which is not to say we're bad on ARM, of course).
multi-hundred ms is slow....
But what is strange to me we have to go through a magnitude of handles and paralleling a browser engine to get to sub 100ms layout. Could we not further improve the current engine?
