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
