Firefox Gets Massive JavaScript Performance Boost

monkeymonkey writes "Mozilla has integrated tracing optimization into SpiderMonkey, the JavaScript interpreter in Firefox. This improvement has boosted JavaScript performance by a factor of 20 to 40 in certain contexts. Ars Technica interviewed Mozilla CTO Brendan Eich (the original creator of JavaScript) and Mozilla's vice president of engineering, Mike Shaver. They say that tracing optimization will 'take JavaScript performance into the next tier' and 'get people thinking about JavaScript as a more general-purpose language.' The eventual goal is to make JavaScript run as fast as C code. Ars reports: 'Mozilla is leveraging an impressive new optimization technique to bring a big performance boost to the Firefox JavaScript engine. ...They aim to improve execution speed so that it is comparable to that of native code. This will redefine the boundaries of client-side performance and enable the development of a whole new generation of more computationally-intensive web applications.' Mozilla has also published a video that demonstrates the performance difference." An anonymous reader contributes links the blogs of Eich and Shaver, where they have some further benchmarks.

Comments

As fast as C code???

[ACDChook]

Correct me if I'm wrong, but generally speaking, I was always under the impression that, as an interpreted language, javascript will never be able to run 100% as fast as natively compiled C code.

Re:As fast as C code???

[BZ]

For what it's worth tracemonkey is about the same speed as unoptimized C on integer math at this point. The difference is register allocation (which tracemonkey doesn't do yet).

Moving to more complicated examples, things get more interesting. Since the jit has full runtime information, it can do optimizations that a AOT compiler cannot do. At the same time, the lack of a type system does hurt, as you point out. At the moment, tracemonkey handles this by doing type inference and then if it turns out to be wrong (e.g. the type changes) bailing out and falling back on the interpreter. Turns out, types don't change much.

The real issue for a real-world Javascript program is that most of them touch the DOM too, not just execute JS. And right now tracemonkey doesn't speed that up at all. In fact, it can't jit parts of the code that touch the DOM. Eventually the hope is to add that ability.

Dr. Michael Franz

[tknd]

The theories behind tracing optimization were pioneered by Dr. Michael Franz and Dr. Andreas Gal, research scientists at the University of California, Irvine.

Hey that's my old compilers professor and my school!

This PDF looks like the paper the article is referencing.

Performance is great and all

[MasterC]

I've written my share of JS-heavy apps and the boost will be nice for that. However, my complaints with JS don't lie with performance.

• Tied too much to the browser. JS works great for some (some love it) but syntactically I hate every last part of it. However: web == JS so I have no other option.
• Typing. Yeah, it has types but they're practically worthless. A Number represents a float/double and an integer? Say what?
• Type checking.
• No reflection.
• No dictionary. Sure, you can use an Object as a dictionary but the second someone prototypes it to add root functionality then you've introduced other items in your "dictionary". (I'm looking at you prototype.js)
• Nothing resembling libraries. No dependencies, etc.
• It's bastardized to accommodate the short comings of HTML (drop downs, combo boxes, etc.)
• Obey's Postel's law too much. Error handling and exceptions is a sad state.
• No threading. No locking. Nothing resembling concurrent programming. The more complicated your app the more arbitrary events and multithreading are important.
• No classes. Prototyping & cloning is a neat paradigm for where it fits but so do class-based objects. This isn't just JS I have this problem with. Being able to do both and using the right one where necessary would be great.
• When is the document loaded? And if you have two libraries vying for that event? (See library complaint)
• Since it has no real library support I have to blame the browser for not providing more general functionality. XML parsing, date stuff is abysmal, and other "routine" stuff you do when making web sites.
• Scoping. Scoping is mind-numbingly bad.
• Namespaces (again, see library complaint) are implemented via object nesting, which isn't really namespaces
• Logging and debugging. I haven't delved into the likes of Firebug to see how it works but when the language (again no libraries so I blame the language) itself only provides alert() then it's clear the creators weren't thinking about debugging at all. At least IE natively will let you debug JS!
• Standard dialogs are alert() and confirm(). Anything and everything else you have to roll your own. I really, really don't want to write something for a Yes/No dialog instead of OK/Cancel confirm().
• Drag-and-drop. If you've done it then you know it's no walk in the park.
• Browser identification and JS version identification. Why should I have to jump through hoops, poke & prod things, and guess at what my JS run-time is? Everyone has their own means to detect it and it's absolutely ludicrous. I'm fine if there's no real "standard" but at least give me the variables to know what I'm writing against so I can adequately work with it. (Again tied too close to the browser.) Every language I use frequently has means for me to identify such things.

I think that's enough. I'm sure you could easily argue back but this is my rant about why this boost is not the saving grace to JavaScript.

Basically my point is that performance does not bring JS up another tier. It just prolongs the pain of having a grossly inadequate language for rich application development. JS does have some nice things about it (first-class functions, closures, for(..in..), etc.) but in no way would I consider it "good" for application development.

Step back and realize the movement is pushing applications into the browser. Yes, the same apps that currently use threading; the same apps that have more than 4 input widgets (input, select, radio, checkbox); the same apps that run slow even when written in native code; the same apps that depends on libraries of code; etc. JavaScript, as is, is not The Answer and this performance boost is just a Bluepill in disguise.

That's pretty impressive...

[Anik315]

It would nice to see some demos of this with John Resig's Processing.js. It could definitely use the kind performance boost being discussed here.

In addition to a performance considerations, it would also be nice to have addtional some additional bit depth in JavaScript.

I anticipate JavaScript will continue to be very popular, but there are alot a lot of reasons other than performance that people won't want to use the language for writing desktop applications over C/C++/Java. That said, there have been alot of recent developments that have made me cautiously optimistic about the future of the language along these lines.

Re:Fast as C but uses lots more memory

[CoughDropAddict]

The catch is that you pay two penalties: startup time and memory. Lots of memory: for keeping stats on what needs compiling, trampolines to call in and out of the interpreter vs. JIT native code, and the native code *plus* the byte code.

That JITs automatically incur large memory footprint or startup time penalties is the logical conclusion you come to if you look at the JVM. But the truth is that JITs don't have to suck as much as the JVM does.

For example, take LuaJIT, a JIT for the already-speedy dynamic language Lua. It speeds up Lua roughly 2-5x while starting up in less than 0.01 CPU-seconds and introducing less than 20% memory overhead. It also takes 2-8x less memory and starts up 10x faster than the JVM, despite the fact that Lua is compiling from source, whereas the JVM starts with bytecode.

I've never looked at the source for the JVM, so I can't say just why it takes so many resources, but I can only conclude that it's because Sun just doesn't consider startup time or memory footprint a priority.

Re:Fast as C but uses lots more memory

[ensignyu]

So, really the memory access will be a bottle neck, you can never hope to have your program in cache and it will be much slower than C.

That's not always a given. If we go by the old rule of thumb that 80% of the time is spent in 20% of the code, we could stick that 20% in one place to maximize cache usage. You can even optimize so that if branches that are taken are kept in the cache, and infrequently executed branches are moved out of the way, maybe in a separate page so they can be swapped to disk.

You can do this to a certain degree at compile time, but often you don't know in advance what paths are going to be hot (it might be based on the data) and it may even change as the program runs.

In practice, if someone tells you that Java is faster that C, they're speaking mostly in hypotheticals. Java and another high-level languages encourage so many layers of abstraction that the sheer amount of code that needs to run will probably make it slower than your typical C program. There's also a lot of things, particularly anything that needs to be dynamic, that you can't easily/efficiently compile.

What's interesting is LLVM and .NET, where you can run C/C++ code in an interpreted/JIT-compiled environment. Potentially, with the optimizations mentioned above, you could have C code running in a virtual machine that's faster than statically-compiled C code.

Re:The Greatest Idea

[totally bogus dude]

Sharepoint 2007 is a good example. Editing of the content is via a browser-based interface, which is quite script heavy. What's interesting is just how script heavy it is. While testing on an old laptop we have connected to an external link, I was a bit dismayed at how slow loading our site was. I got the impression that the browser was pausing before displaying the page for some reason.

Opening up task manager, I saw that before IE displayed the page, it would spin on 50% CPU (on an old hyperthreaded P4) for over 5 seconds before finally rendering the page. After some experimenting which yielded consistent results, I tried Firefox and the difference was dramatic, to say the least.

The upshot of all this is that we may need to recommend to our clients that they use Firefox to edit their Sharepoint 2007 sites, because it provides a significantly better experience than IE does if you have older hardware. On my own desktop at work (a reasonably modern Core 2 Duo) IE does spike the CPU usage, but generally it's for less than a second or two so it's not really distracting. Firefox is faster, but both are quick enough that it doesn't make a real difference to a human.

Completely off-topic: I used refreshes of the task manager process listing to judge how long IE was spinning for. I always assumed the default setting was to refresh the list once per second, and some quick testing now confirms that that is what it does. If you go to View -> Update Speed, the default setting is "Normal". The status tip for this setting says "Updates the display every two seconds". Clearly a lie - or is it? If you select "Normal", then the display does in fact update every two seconds, and there doesn't seem to be any way to get it to go back to refreshing once per second.

C is inefficient

[speedtux]

You are ABSOLUTELY wrong! C# by its very nature can not be as fast as C.

The C# JIT has all the information that a C compiler has (essentially, the entire source code). In addition, it has a lot of global program information and it has runtime statistics. And, the C# language has better defined semantics. All of this taken together means that C# can be optimized better than C.

In terms of performance, C is a lousy language; Fortran is a "faster language" than C.

The only reason C even runs as well as it does is because people have invested 20 years in making compilers squeeze out the last cycle, because C compilers play fast and loose with C semantics at high optimization, and because even CPUs have been tuned to accommodate its semantics.