860980 - performance.now is 2x-5x slower than Date.now

Status: RESOLVED DUPLICATE of bug 824495

(Core :: JavaScript Engine, defect)

Description

[:Harald Kirschner :digitarald]

Run http://jsperf.com/new-date-vs-date-now-vs-performance-now/5

Even though good performance is implied by the namespace, Date.now is much faster than performance.now.

If game developer see this test they might prefer Date.now as they fear performance implications.

Not sure if this is a JavaScript Engine bug.

Comment 1

[Boris Zbarsky [:bzbarsky]]

I updated the testcase to separate out the effects of getting the performance object from calling now() on it.  See http://jsperf.com/new-date-vs-date-now-vs-performance-now/6

With that change, the "Cached performance object" test runs at the same speed for me, on Mac, as the "Date.now" test.  See also bug 824495 and the data there.

Is there something in this bug that's not covered by bug 824495 and is dependencies?

Comment 2

[Boris Zbarsky [:bzbarsky]]

And note that performance.now() has to produce higher quality results than Date.now(), which does mean that in many cases it will in fact take longer to run (esp. on Windows), even if you ignore the slowness from the "performance" getter...

Comment 3

[:Harald Kirschner :digitarald]

Seems (In reply to Boris Zbarsky (:bz) from comment #1)
> Is there something in this bug that's not covered by bug 824495 and is
> dependencies?

Seems like Vlad got the gist, and your "fix" to cache the property works wonders and shows that the problem is just the window property access.

Comment 4

[Avi Halachmi (:avih)]

FYI, these are the numbers on my system (Windows 7-64, i7-3630qm) with a nightly which I updated just now:

Date.now();           3,009,581 ±0.30 %69% slower

+new Date();          1,439,573 ±0.77% 85% slower

performance.now()     2,569,185 ±1.07% 74% slower

new Date().getTime()  2,388,121 ±0.95% 76% slower

new Date().valueOf()  2,390,906 ±0.38% 76% slower

Cached performance object
perf.now()            9,845,328 ±0.15%     fastest