940815 - Browsermark "DOM Search" is 1.6x slower than Chrome

Status: NEW

(Core :: JavaScript Engine, defect)

Description

[Chris Peterson [:cpeterson]]

From Naveed's Browsermark "DOM Search" test results (bigger is better):

* Chrome 31 = 8,144
* Chrome 27 = 7,848
* Firefox 25 = 5,195
* Firefox 22 = 5,260
* IE11 = 10,461

Firefox 25 is slightly slower than Firefox 22.

Comment 1

[Boris Zbarsky [:bzbarsky]]

On trunk, we're close to parity, I think.  Fixing bug 820848 would help even more, maybe.

One interesting feature here is that we end up with 11% of our time under jit::DoGetPropFallback.  In the end it ens up doing a get on the HTMLDocument, but via all the proxy machinery, not the IC.  I'll look into what property exactly and why.

Another 8% is js::GetProperty, again falling into the proxy machinery, again not via the IC.

15% of the time is under regexp_exec.  The vast majority of this is CreateRegExpMatchResult and the DefineGeneric calls it does.  In fact, smells a lot like bug 879402.  And bug 876846 (which is not surprising; the latter has code similar to this benchmark).

25% of the time is under array_slice. 1/4 of this is SetArrayElement, and about half is going through the proxy getElementIfPresent machinery on an HTMLCollection.  That's bug 697343.

Again, mostly seems like a JS testcase...

Comment 2

[Boris Zbarsky [:bzbarsky]]

> jit::DoGetPropFallback

I expect this is the same issue as we found in bug 922071.  

> Another 8% is js::GetProperty

Also as discussed in bug 922071.

Comment 3

[Boris Zbarsky [:bzbarsky]]

So for me, in a build with bug 879402 fixed, I see numbers kinda like:

Firefox nightly: 9240
Chrome dev: 6516

For comparison, fx26: 4026
Nightly without bug 879402: 8208

A profile of the nightly with bug 879402 fixed shows:

* 18% of the time under array_slice, of which 12% is in the HTMLCollectionBinding code.  
* 10% under array_push 
* 10% under js::GetProperty
* 9% under regexp_exec, breaking down as 6% CreateRegExpMatchResult (half of this is
  malloc under createArray!) and 3% ExecuteRegExp.
* 5% jit::DoGetPropFallback.
* 4% js::SetObjectElement
* 2% calling getElementById
* 2% calling getElementsByTagName
* 3% CloneRegExpObject
* 3% CreateThisForFunctionWithProto

and some long-tail stuff (e.g. js_Date is popping up at 1% now).