Well then, as has been mentioned, your best bet is to preallocate the maximum number of these objects you need and manage them yourself. As long as you have a reference to them, as in a free (linked type) list, they can't really be garbage collected.
I've seen some optimized compiled code posted and it's considerably more instructions and CPU cycles than someone would code by hand, or even what a good C/C++ compiler might optimize. This was for a very simple loop that would be coded in maybe 5 or 6 instructions in assembly language by hand, but was maybe 30-50 instructions optimized and compiled by V8. I'm not saying V8 is bad, it's just really hard to optimize further (perhaps) because JavaScript is so dynamic. If you weren't running in the browser, I can think of several tricks you could do, like managing your 2d vectors in C++ code and exposing them as opaque type handles to the JavaScript so you can do the bulk of your logic in JavaScript and the stuff that needs to be really fast in C++. Good luck. On Dec 25, 2011, at 7:44 PM, Joseph Gentle wrote: > It will be, yeah. I'm benchmarking using nodejs and v8 on the command > line though. > > -J > > > On Mon, Dec 26, 2011 at 2:29 PM, Michael Schwartz <[email protected]> wrote: >> This code is running in the browser? >> >> On Dec 25, 2011, at 7:27 PM, Joseph Gentle wrote: >> >>> Cool - well, from inlining a bunch of vectors, and some other minor >>> tweaks I've nearly doubled performance. Its still >3x worse than the >>> original C implementation though, so I think I can do better. Brendan: >>> local numbers should be stored on the stack, right? >>> >>> According to this profiling run: https://gist.github.com/1520465 : >>> >>> I'm spending 45% of my time in this javascript function: >>> https://github.com/josephg/Chipmunk-js/blob/master/lib/cpArbiter.js#L349-406 >>> >>> Even a 2% improvement in that one function there would be noticable. >>> Any ideas on how I can improve it? (The array I'm looping over usually >>> only has one element, if that helps). >>> >>> I'm also spending 10% of my time in this C++ function: >>> v8::internal::SemiSpaceIterator::Next >>> What is that? Can I do less of it? >>> >>> >>> I really appreciate the help - physics in the browser is fun! - >>> http://dl.dropbox.com/u/2494815/code.html >>> >>> -Joseph >>> >>> >>> On Mon, Dec 26, 2011 at 6:08 AM, Brendan Miller <[email protected]> >>> wrote: >>>> I could be wrong, but I think I asked on this list earlier, and locals >>>> are not necessarily stored on the stack because they can be captured >>>> by a nested function. So, depending on how much you use closures, >>>> inlining might not solve your problem. >>>> >>>> On the other hand a simple free list would make a lot of sense and >>>> would presumably lead to more readable code. Certainly, this is what >>>> I'd do in C or C++ if I wanted to reduce allocation and deallocation >>>> time. In javascript, the effect would be a little bit different. On >>>> the first compaction, I think you wouldn't save much time, but once >>>> your vectors got promoted into the "old" generation, they'd see fewer >>>> compactions. >>>> >>>> I'm not a v8 developer though and don't know the internals of the GC, >>>> except that it is generational. >>>> >>>> On Sat, Dec 24, 2011 at 10:48 AM, tjholowaychuk <[email protected]> >>>> wrote: >>>>> I would inline most of the simple ones personally, or even maybe add a >>>>> build step and use some kind of macro >>>>> >>>>> On Dec 24, 1:37 am, Joseph Gentle <[email protected]> wrote: >>>>>> I'm porting a physics engine (chipmunk!) from C to javascript. >>>>>> Internally, >>>>>> chipmunk uses 2d vectors pretty extensively. In C, they're a simple >>>>>> struct >>>>>> passed by value. In javascript, my vectors are being allocated on the >>>>>> heap. >>>>>> >>>>>> I did some benchmarks - in 5 seconds, chipmunk-js allocates about 20 >>>>>> million vectors. The simulation spends about a third of its time in the >>>>>> garbage collector. (Eep!). >>>>>> >>>>>> I would move across to simply storing x and y values, but a lot of the >>>>>> vector manipulation functions need to return new vectors. (Eg, add(), >>>>>> mult(), rotate(), lerp(), ... etc). If I store (x,y), I need a way to >>>>>> return two values from those functions. >>>>>> >>>>>> My ideas: >>>>>> - Try and use an object pool of vectors. It might be hard to track the >>>>>> lifetime of all the vectors the library uses, but I should be able to >>>>>> manually release most of them. >>>>>> - Make all the functions that return a vector instead store the (x,y) >>>>>> pair >>>>>> in a pair of global variables. Other functions can then copy the result >>>>>> back when they're done computing. That way, I can remove heap-stored >>>>>> vectors entirely; though my code will get super messy. >>>>>> - Manually inline a lot of the vector functions. Again, my code will get >>>>>> messier. >>>>>> >>>>>> What do you guys reckon? Are there any other options? >>>>>> >>>>>> My trivial vector implementation is >>>>>> here:https://github.com/josephg/Chipmunk-js/blob/master/lib/cpVect.js >>>>>> >>>>>> -J >>>>> >>>>> -- >>>>> v8-users mailing list >>>>> [email protected] >>>>> http://groups.google.com/group/v8-users >>>> >>>> -- >>>> v8-users mailing list >>>> [email protected] >>>> http://groups.google.com/group/v8-users >>> >>> -- >>> v8-users mailing list >>> [email protected] >>> http://groups.google.com/group/v8-users >> >> -- >> v8-users mailing list >> [email protected] >> http://groups.google.com/group/v8-users > > -- > v8-users mailing list > [email protected] > http://groups.google.com/group/v8-users -- v8-users mailing list [email protected] http://groups.google.com/group/v8-users
