1821137 - EmberJS-TodoMVC spends a lot of time in js::NativeObject::ensureDenseElements during addToListeners

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, task, P2)

Description

[Markus Stange [:mstange]]

In the function addToListeners in the EmberJS-TodoMVC benchmark, we spend 2250 samples inside Array.prototype.push versus V8's 121 samples.

To reproduce, run index.js inside https://github.com/mozilla/Speedometer/tree/ab0e3b8406bbc0356244f8cd430900e9a346737b/resources/todomvc/architecture-examples/emberjs/dist in the JS shell.

Profiles (focused on addToListeners's "JS-only self time"):
Spidermonkey: https://share.firefox.dev/3LaxwBU
V8: https://share.firefox.dev/41VPJJr

A lot of Spidermonkey's push time is spent in ensureDenseElements.

Comment 1

[Jan de Mooij [:jandem]]

We spend a fair amount of time growing the dense elements. There's also some slots store buffer time.

Comment 2

[Olli Pettay [:smaug][[e-mail]]]

EmberJS has been removed from sp3. Does the issue show up in other tests?

Comment 3

[Markus Stange [:mstange]]

I haven't seen it stand in other tests. I'll reopen this bug if I find evidence that it matters.