940817 - Browsermark "JavaScript Array Weighted" is 1.6x slower than Chrome

Status: RESOLVED INCOMPLETE

(Core :: JavaScript Engine: JIT, defect, P4)

Description

[Chris Peterson [:cpeterson]]

From Naveed's Browsermark "JavaScript Array Weighted" test results (bigger is better):

* Chrome 31 = 10,493
* Chrome 27 = 10,234
* Firefox 25 = 6,450
* Firefox 22 = 6,332
* IE11 = 8,569

Is this the same issue as Peacekeeper arrayWeighted bug 918746?

Comment 1

[Sean Stangl [:sstangl]]

Peacekeeper arrayWeighted is:
> www.peacekeeper.therichins.net/js/tests/array/arrayWeighted.js

Browsermark arrayWeighted is:
> http://browsermark.rightware.com/tests/benchmarks/javascript/array_weighted/test.js

The tests are similar (one clearly copied from the other), but not identical. Browsermark's involves JQuery in the execution loop, while Peacekeeper's version is more straight-line.

Note that these JS tests should be ultra-low-priority, since reaching parity with Chrome does not have significant effect on Browsermark total score. Resources would be best put toward the graphics/html5_canvas and css/3d_rendering tests.

Comment 2

[Sean Stangl [:sstangl]]

The majority of time is spent in test.js:112, on the following line:

> var chars = selectedCountry.splice(0, count).join("");

The code is attempting to get a string without the first |count| characters. It does so by splitting the initial string into a character array, calling splice() to remove the first |count| members of the array, and joining the characters back into a string.

Sigh.

V8 handles splice() better, probably because the temporary arrays always hit their nursery. Additionally, they have no performance penalty from the join() -- we could have similar behavior by using a RopeBuilder instead of StringBuffer in array_join().

Comment 3

[Sean Stangl [:sstangl]]

Just in case someone from Browsermark is reading this bug, note that all the array nonsense can be replaced by the one-liner |str.substring(count)|.

Comment 4

[Lars T Hansen [:lth]]

Test case gone, and we have generational GC now.