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Firefox 18 Beta Out With IonMonkey JavaScript Engine
An anonymous reader writes with a quick bite from The Next Web about the latest Firefox beta, this time featuring some under-the-hood improvements: "Mozilla on Monday announced the release of Firefox 18 beta for Windows, Mac, and Linux. You can download it now from Mozilla.org/Firefox/Beta. The biggest addition in this update is significant JavaScript improvements, courtesy of Mozilla's new JavaScript JIT compiler called IonMonkey. The company promises the performance bump should be noticeable whenever Firefox is displaying Web apps, games, and other JavaScript-heavy pages."
javascript was never meant to do the things it's being used for now, that's why sites are so damned slow now.
What sites are so damned slow? It's not the Javascript in most cases, it's the asset loading. The tubes are still the bottleneck on the web.
If anything, Javascript is speeding things up. AJAX content updates without a full page refresh are commonplace now, and there are more and more sites that are mostly client-side, using frameworks like Backbone.
I haven't kept track with the JIT's that have been in Firefox. I recall the days when TraceMonkey and JagerMonkey were added to boost performance. Could somebody recap or tell why Firefox is abandoning the older versions or redoing them? I'm truly curious as to what they learned, what worked and what didn't work. Are they finding new usage patterns that warrant a new JIT design? Thanks.
Its good to see the focus of this release being an attempt to increase javascript speed by leaps and bounds. Modern webpages often use JS that goes way beyond anything people did 10 years ago (Jquery for example) and the complexities of what people do with javascript noticably slow down most webpages considerably.
http://interserver.net/
Well, let's see. Go to a site like Engadget and make sure your javascript allow settings are set to show the page comments. Now open 24 hour's worth of news postings in tabs. After about halfway through, your browser will start to lag with CPU pegged. It's not loading content off the Internet if your CPU is pegged. But it's just all the instances.
Or you can replicate it with a busy thread like one of their "post a comment to enter in a draw), where it gets around 200 comments a minute. You'll find the browser noticably slows down as the javascript is constantly running.
Repeat same with a site like Gizmodo (probably an even worse offender). I can't open more than 10 tabs at a time before the browser locks up for a few minutes at 100% CPU.
Latest firefox and Chrome. Websites just gobble up the Javascript processing. Those sites are unusable on weaker javascript engines.
Wikipedia goes into a bit of detail about it but in basic summary...
TraceMonkey was the first JIT compiler for SpiderMonkey released in Firefox 3.5.
JagerMonkey is a different design on TraceMonkey which outperforms it in certain circumstances (Some differences between TraceMonkey and JagerMonkey)
IonMonkey is another attempt at better perfecting the idea of JagerMonkey allowing even greater optimisations under particular circumstances.
However TraceMonkey, JagerMonkey and IonMonkey are part of SpiderMonkey as JIT compilers, not a replacement of SpiderMonkey itself.
Engadget has heavily linked in components from other websites in the form of inline-frames , advertisement, images, tracking etc. They have also heavily used Javascripts, transparent layers etc. One would think they purposefully applied "worst practices".
Having either DNT+ or AdBlock (with privacy filters) will stop the commenting system altogether.
Slashdot is a prime example of a site heavily using javascript.
Ubuntu 10.04 LTS stuck to Firefox 3.6 for a long time. When loading a /. page, particularly one with many comments, it often gave me the "script is taking too long to complete" warning message. It would eventually complete, but took long. When Ubuntu finally replaced the browser with a newer Firefox, that problem was solved. It now renders reasonably fast.
And considering I have ads disabled, it is really /. itself that's so demanding.
A short summary:
1) TraceMonkey turned out to have very uneven performance. This was partly because it type-specialized very aggressively, and partly because it didn't deal well with very branchy code due to trace-tree explosion. As a result, when it was good it was really good (for back then), but when it hit a case it didn't handle well it was awful. JaegerMonkey was added as a way to address these shortcomings by having a baseline compiler that handled most cases, reserving tracing for very hot type-specialized codepaths.
2) As work on JaegerMonkey progressed and as Brian Hackett's type inference system was being put in place, it turned out that JaegerMonkey + type inference could give performance similar to TraceMonkey, with somewhat less complexity than supporting both compilers on top of type inference. So when TI was enabled, TraceMonkey was switched off, and later removed from the tree. But keep in mind that JaegerMonkey was designed to be a baseline JIT: run fast, compile everything, no fancy optimizations.
3) IonMonkey exists to handle the cases TraceMonkey used to do well. It has a much slower compilation pass than JaegerMonkey, because it does more involved optimizations. So most code gets compiled with JaegerMonkey, and then particularly hot code is compiled with IonMonkey.
This is a common design for JIT systems, actually: a faster JIT that produces slower code and a slower JIT that produces faster code for the cases where it matters.
https://blog.mozilla.org/dmandelin/2011/04/22/mozilla-javascript-2011/ has a bit of discussion about some of this.
aaaand I'll be abel to boot Linux faster!
I don't understand why this comment got +5. It is pretty misguided.
The statement:
> I realized, you can't speed up assembly language -- It's a perfectly optimized language, there's nothing under the hood to tweak
makes some limited sense in some contexts (one could argue that the microcode supporting the assembler on the CPU is repeatedly optimized), but none in this. The IonMonkey JIT does essentially optimize the assembler code[*], by rearranging it in various ways to make it faster. E.g. it takes stuff like this (in javascript, as I have not written assembler in years):
for ( var i = 0; i != 10 ; ++ i ) {
var foo = "bar";
}
and changes it to e.g. this:
for ( var i = 0; i != 10; ++i ) {
}
var foo = "bar";
possibly then this:
var foo = "bar";
This is an optimization and it is performed at assembler level (Again: the above is not meant to be read as JavaScript, but assembler).
The other statement that really sticks out is this:
> A sign of a horribly designed language is that the speed of its implementations can be repeatedly increased "by leaps and bounds"...
This simply highlights that the poster really do not understand the goals behind crossplatform languages, such as Java, Dalvik, JavaScript, lisp, ML, Python, Perl, and so on, or the goals for weakly typed languages.
[*] It works on an abstract representation of the assembler code, but it might as well have been working directly on the assembler, was it not for the fact that this would require it to learn to many assembler variants.