FS#27673 - [firefox] JavaScript Performance Much Slower Than Expected

Attached to Project: Arch Linux
Opened by Martin (mumart) - Thursday, 22 December 2011, 19:10 GMT
Last edited by Andrea Scarpino (BaSh) - Monday, 09 January 2012, 14:02 GMT
Task Type Bug Report
Category Packages: Extra
Status Closed
Assigned To No-one
Architecture i686
Severity Low
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 0
Private No

Details

Description:

Firefox 9 is claimed to have "significantly improved" JavaScript performance over previous versions:

http://www.mozilla.org/en-US/firefox/9.0/releasenotes/

I am experiencing a very low V8-benchmark score of 143 in Firefox 9, compared with 815 from Firefox 8 on the same system. The performance is roughly the same if I disable the JIT using "about:config", suggesting the JIT is permanently disabled.

Steps to reproduce:

Visit "http://v8.googlecode.com/svn/data/benchmarks/v6/run.html" and observe low score.
This task depends upon

Closed by  Andrea Scarpino (BaSh)
Monday, 09 January 2012, 14:02 GMT
Reason for closing:  Not a bug
Additional comments about closing:  see the last comment
Comment by Ionut Biru (wonder) - Thursday, 22 December 2011, 19:15 GMT
my score on i686 is Score: 4346
Comment by Jan de Groot (JGC) - Thursday, 22 December 2011, 19:42 GMT
As scores are quite low anyways on your system, that probably indicates a low-spec system. What CPU and how much memory do you have?

My guess is that the new Type Inference option in the javascript engine uses more memory which you system doesn't have. Could you re-run the test with javascript.options.typeinference set to false?
Comment by Martin (mumart) - Thursday, 22 December 2011, 22:57 GMT

I disabled "type inference" and the JIT is now working. The V8 score is now back up to 750, and I can run my synthesizer in real time again. Thanks for your help!

The system an old 1600mhz Athlon XP with 1GB of RAM. So yes, low spec. That's why I run Arch :)
Comment by Pierre Schmitz (Pierre) - Friday, 23 December 2011, 05:36 GMT
It could be indeed memory related. I tested this benchmark on my super-slow Intel Atom with 1.6GHz (x86_64) and got a score about 1120. Overall memory usage went up to 950MB (I have 2GB installed).
Comment by Martin (mumart) - Friday, 23 December 2011, 16:48 GMT
I have increased my RAM to 1.5GB but still cannot enable type-inference. My CPU does not have SSE2 instructions, so that could be a possible cause. I was under the impression that the same back-end assembler is used whether type-inference is enabled or not, though.

Either way, if my system cannot support type-inference, I don't think it should be automatically disabling the entire JIT.

EDIT: I am getting the same behaviour in Windows XP on this system, so I'll ask around.
Comment by Ionut Biru (wonder) - Friday, 23 December 2011, 18:25 GMT
we cannot do anything regarding your issue. Please forward this bug to http://bugzilla.mozilla.org
Comment by Martin (mumart) - Friday, 23 December 2011, 22:32 GMT
Of course! Thanks again for all your help.

It looks like Mozilla is dropping support for JIT-compilation on non SSE2 CPUs. I've found the bug upstream at https://bugzilla.mozilla.org/show_bug.cgi?id=712261

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