LuaJit 2.0 is out

http://luajit.org/download.html

by nickik • 14 years ago

172 72 14 years ago

luajit.org

zdw• 14 years ago

There have also been a few changes in the roadmap for LuaJIT, as announced here:

http://www.freelists.org/post/luajit/LuaJIT-Roadmap-20122013...

dbaupp• 14 years ago

Changelog: http://luajit.org/changes.html (extremely detailed)

pdog• 14 years ago

I understand that for LuaJIT 2.0, the whole VM has been rewritten. What's changed? What's new?

dmpk2k3• 14 years ago

If you're referring to LuaJIT 1 vs 2, the big differences are that LuaJIT 2 has a trace-tree JIT, and interpreters for each platform written in assembly. The improvement in performance is significant: LuaJIT2's interpreter alone is faster than LuaJIT1's JIT.

It's hard to compare LuaJIT1 and 2, since LuaJIT2 is the most advanced JIT for a dynamically-typed language on the planet. The performance it can achieve with zero type annotations still blows me away.

wesm• 14 years ago

Careful, you might hurt some people's feelings. Has anyone done a systematic comparison of LuaJIT's performance with PyPy's?

eslaught• 14 years ago

I think you're forgetting the gold standard in dynamic languages from the 80s: Common Lisp. It's still around, and it's still faster than almost every other dynamically typed language out there.

http://shootout.alioth.debian.org/u64/benchmark.php?test=all...

Half of the benchmarks are less than a factor of 2x slower than C, which is better than even GHC can do for Haskell.

Edit: Disclaimer: http://shootout.alioth.debian.org/dont-jump-to-conclusions.p...

rayiner• 14 years ago

Pedantry: it's actually not a trace-tree JIT. It doesn't treat traces as trees. See: http://lambda-the-ultimate.org/node/3851#comment-57679

sshumaker• 14 years ago

Also the addition of the ffi library. It totally changes the way you integrate with C code (for the better) - its the best FFI I've seen in any language.

erichocean• 14 years ago

The Factor FFI is pretty similar.

spicyj• 14 years ago

Huge congrats to Mike Pall on the release. The man is a machine when it comes to this sort of thing.

alberth3• 14 years ago

HUGE congrats to Mike Pall. No amount of praise to him is enough.

Hopefully, sponsors will continue to donate to this project to keep Mike fully employed and ensure long-term commitment of this project.

I encourage sponsors to considered donating [1]

On a side note, I wish the Programming Language Shootout [2] would add back in LuaJIT to demonstrate just how fast LuaJIT is in comparison to other languages. It's just amazing.

[1] http://luajit.org/sponsors.html

[2] http://shootout.alioth.debian.org/

_casperc• 14 years ago

Are there any other current benchmarks around for LuaJIT vs for instance java?

alberth3• 14 years ago

When then Programming Language Shootout use to include LuaJIT, it had a benchmark against Java.

If you want to see just LuaJIT vs Lua, [1] is a good comparison.

The reason why I liked the inclusion of LuaJIT in the Programming Language Shootout was that it compared LuaJIT to other language implementations not just on speed, but memory consumption and lines of code. All of which, LuaJIT typically dominated.

[1] http://luajit.org/performance_x86.html

abecedarius2• 14 years ago

https://github.com/darius/superbench is not a big fancy cross-language shootout, at all, but I tried a few little programs I actually cared about. LuaJIT 'won' in the sense that of the languages I tried it had the best combo of performance and pleasant productivity, informally. I didn't try to quantify the latter.

(Also, no Java because I wouldn't seriously consider it for hacking-for-fun.)

igouy• 14 years ago

On a side note, I wish there was more doing and less wishing others would do :)

http://shootout.alioth.debian.org/more.php#languagex

gavinlynch• 14 years ago

Something tells me there is an MC Hammer joke in here regarding being 2.0-Lua-Jit-To-Quit, but I'm not sure I can find the phrasing to excite the level of humor I was hoping for...

Oh well, congrats on the release anyway! :)

hyuuu• 14 years ago

haha nice, this is like, one version only joke, once they hit 2.1, that wont fly

StavrosK3• 14 years ago

2.1-Lua-Jit-To-Quit-.1

nickik9• 14 years ago

I wish I could understand LuaJit completly. I think if there is any (reasonably sized) software I would like to completly understand its this one.

There is not only lots of good algorithms but also a lot of fantastic engineering. Things that you can not learn by reading papers.

Congrats Mike Pall. Now lets see if you can do the same for GC community that you did to the JIT community. Good Luck.

chubot• 14 years ago

Yeah I agree it's a very interesting piece of software.

But do you understand the prequisites -- namely processor microarchitecture? I know that's why I don't understand it. I imagine if I did it might not be that hard to understand.

Most people's knowledge of the stack stops somewhere around C. C hasn't changed for 40 years. It's a portable assembly language, i.e. the common mental model is that each construct in C is a handful of assembly instructions on any processor. But to get LuaJIT-type performance you have to understand exactly how the CPU works, i.e. pipelining and reordering, internal caching algorithms, internal branch prediction algorithms, and maybe to some extent multicore, although I guess LuaJIT is single-threaded like Lua.

Mike Pall's mental model is for sure not C (since a lot of it isn't even written in C), but the lower level CPU architecture. And that has changed a lot in the last 10 years. I think even if you coded a lot of assembly language in the 80's it wouldn't necessarily translate to working on something like LuaJIT. My impression from skimming some online posts is that he has read hundreds of pages of Intel/ARM reference documentation from cover to cover, for multiple CPUs. I think there are a limited number of people with the patience to do that, since it's non-portable and changes relatively quickly.

Another problem is I think that the open source tools that are available don't work at the right level. Like when you are running profilers, they are helping you profile assembly code generated by a C compiler. The performance characteristics he's taking advantage of are at a lower level. I think you need CPU-specific performance counters and so forth, and there's a different way of getting those for each make/model. Are there even open source tools that allow you to get this information? I'd appreciate a pointer.

It's just a different level of abstraction than most programmers are working with. Not that many people are even writing "low level" C these days, e.g. something like redis. A lot of "application level" C code you see these days is old and/or not particularly fast.

I would be interested if anyone has any pointers for this style of code other than "read a bunch of CPU manuals". :)

daurnimator3• 14 years ago

"Another problem is I think that the open source tools that are available don't work at the right level. Like when you are running profilers, they are helping you profile assembly code generated by a C compiler. The performance characteristics he's taking advantage of are at a lower level. I think you need CPU-specific performance counters and so forth, and there's a different way of getting those for each make/model. Are there even open source tools that allow you to get this information? I'd appreciate a pointer."

The way forward is a sampling profiler.

By sampling the stack every (eg) millisecond, you can build a picture of what is taking the longest.

nickik9• 14 years ago

> But do you understand the prequisites -- namely processor microarchitecture?

I do not but I try to learn more about that (coursera ftw).

LuaJit is awesome on many level, first as you have pointed out attention to detailed on processer level is quite special and not many people can do that.

Other then the good usage of the processor is not the only reason luajit is fast. On the compiler level, the optimization luajit does are extensive. Even lots of novel innovations are in that that people writting papers should read (Mike Pall has posted a list of thing that he thinks are somewhat novel). The nature of the trace compiler makes many of these things less complicated then they would have been otherwise.

aidenn0• 14 years ago

"Are there even open source tools that allow you to get this information? I'd appreciate a pointer."

http://icl.cs.utk.edu/papi/

haberman• 14 years ago

I think that most sampling profilers like oprofile (http://oprofile.sourceforge.net/news/) or perf (https://perf.wiki.kernel.org/index.php/Main_Page) will give you CPU-level profiling and performance counters. The UI of those tools isn't super-friendly; if you're on OS X the "Instruments" app gives the same information with a far superior UI.

I have written a JIT that uses LuaJIT's dynamic assembly language engine DynASM (http://luajit.org/dynasm.html). DynASM is an incredibly piece of engineering, it lets you write really readable code for generating machine code at runtime, and is extremely small and low-overhead.

I keep meaning to write an article that demonstrates how to use LuaJIT for a small but interesting JIT. I just never quite get around to it. I always wish that I could use to implement the Universal Machine from ICFP 2008 (http://www.boundvariable.org/task.shtml), which is absolutely the most delightful problem ever, but as I recall it makes extensive use of self-modifying code which makes JIT-ting much more difficult and less effective.

sb• 14 years ago

Some hints for your quest:

- Linux's perf tool allows you to read HW performance counters. It's pretty self-explanatory, and some interesting ones are platform-neutral, whereas others you have to specify the CPU manufacturer's hex-code. (See Intel manual, for example.)

- For pipelining and HW/CPU details, I suggest you grab a copy of Hennesy and Patterson's Computer Architecture: A Quantitative Approach. There is also Computer Architecture: A Programmer's Perspective, which is good, but I think for what you're interested in, CAAQA is the better book.

- If you just want to play around with HW performance counters, you might want to try Intel's vtune, which comes (or at least did so, two years ago) as an Eclipse plugin/RCP-workbench.

malkia3• 14 years ago

I would love if someone starts a project - "Reading & Understanding LuaJIT". I've seen a similar project for PostgreSQL.

elliptic• 14 years ago

Have you a link for that?

nickik9• 14 years ago

There are many compiler books but no books about JITs in general. There are some good blogpost about LuaJit but not that many. Following Mike Pall (MikeMike on HN or reddit is intressting too)

This is a good start: http://playingwithpointers.com/archives/1010

Scaevolus• 14 years ago

Mike Pall wrote a brief summary for "Reading & Understanding Lua", which is likely a prerequisite.

http://www.reddit.com/r/programming/comments/63hth/ask_reddi...

mamcx• 14 years ago

Is possible to use this for build a language? (I wanna to create my own language, but hope for something easier than LLVM, java, do it from zero in C)

z3phyr3• 14 years ago

Yeah people are trying to port clojure on LuaJIT.. It is possible.

dmpk2k3• 14 years ago

I'm curious how they map Clojure's persistent data structures with many threads onto Lua states.

graue• 14 years ago

I got curious and looked into this. The relevant effort seems to be this, a new backend for the ClojureScript compiler which compiles to Lua instead of JavaScript:

https://github.com/raph-amiard/clojurescript-lua

http://raph-amiard.github.com/ClojureScriptLua.html

fusiongyro• 14 years ago

I'd be surprised if it were easier than LLVM, which is pretty easy.

But if you want to make a language you should absolutely not get hung up on technology. Even though it's very dated, Crenshaw's "Let's Build a Compiler" can teach you everything you need to get started building languages from scratch and by hand, and it moves pretty fast too:

http://compilers.iecc.com/crenshaw/

There are other tutorials out there which will get you places. The first thing to do, really, is make a sketch of the language as you'd like to use it, and get excited about that, and then sit down and implement bits of it at a time. Compiler/interpreter writing is extremely rewarding—you get a lot of payback for your investment. Good luck!

someone13• 14 years ago

Yes, totally possible! For example, see MoonScript, a CoffeeScript-like language that compiles to Lua:

http://moonscript.org/

jd• 14 years ago

It's actually really easy to take the JIT-compilation engine from LuaJit and use it for the compiler of your own programming language. The LuaJIT code is surprisingly modular, and you can pretty much take what you need.

For scanner/parser generation Lemon and Ragel are terrific. That takes care of building the AST for you. LuaJIT does the heavy lifting and takes care of the architecture specific edge cases. That just leaves the fun part in the middle where you decide on the semantics and syntax of your language.

minikomi3• 14 years ago

What are people using LuaJit for in the wild?

Particularly interested in Android integration - has anyone used it for any projects? From my admittedly small experience using it, I love the language, and would really like to use it in some way practically.

StavrosK3• 14 years ago

I'm using it for http://www.instahero.com/. Not mobile development, but I love the speed and sandboxing features.

minikomi3• 14 years ago

Thanks for the reply!

How are you using it? With a lua web framework, or more low level stuff?

edit: great looking site btw.

comex• 14 years ago

I'd like to use Lua, partly to take advantage of LuaJIT and partly because it's an interesting language, but it drives me crazy that it lacks things like 'continue' and '+='. Maybe I should use MoonScript, but that completely discards Lua's aesthetics, which is hardly better.

fuzzythinker• 14 years ago

moonscript to the rescue! http://moonscript.org/reference/#update_assignment

pheon• 14 years ago

modify the luajit frontend. Added continue and != and some other weirder syntactic sugar, was only a half dozzen lines of code.

catwell• 14 years ago

Lua 5.2 added "goto", which basically solves the lack of "continue". LuaJIT supports it too.

moe• 14 years ago

I wonder if a kickstarter could convince him to look at a Ruby VM ;)

riffraff• 14 years ago

well, he does have plans until luajit3... maybe we can book him in advance? I'd still like a fast ruby in five years :D

ksec• 14 years ago

May be someone should work on Ruby to Lua instead? Using Lua and LuaJIT as a underlying languages. Like Coffescript to Javascript.

That would be a lot faster then working on Ruby VM. And since Ruby 2.0's VM is still as slow as hell compared to LuaJIT

LuaJit 2.0 is out

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