Optimization of a GC language, any ideas?

Question

I'm a pretty big newbie when it comes to optimization. In the current game I'm working on I've managed to optimize a function and shave about 0.5% of its CPU load and that's about as 'awesome' as I've been.

My situation is as follows: I've developed a physics heavy game in MonoTouch using an XNA wrapper library called ExEn and try as I might I've found it very hard to get the game to reach a playable framerate on an iPhone4 (don't even want to think about iPhone3GS at this point).

The performance degradation is almost certainly in the physics calculations, if I turn physics off the framerate jumps up sharply, if I disable everything, rendering, input, audio and just leave physics on performance hovers around 15fps during physics intensive situations.

I used Instruments to profile the performance and this is what I got: http://i.imgur.com/FX25h.png The functions which drain the most performance are either from the physics engine (Farseer) or the ExEn XNA wrapper functions they call (notably Vector2.Max, Vector2.Min).

I looked into those functions and I know wherever it can Farseer is passing values by reference into those functions rather than by value so that's that covered (and it's literally the only way I can think of. The functions are very simple themselves basically amounting to such operations as

return new Vector2(Max(v1.x, v2.x), Max(v1.y, v2.y)) 

Basically I feel like I'm stuck and in my limited capacity and understanding of code optimizations I'm not sure what my options are or if I even have any options (maybe I should just curl into a fetal position and cry?). With LLVM turned on and built in release I'm getting maybe 15fps at best. I did manage to bring the game up to 30fps by lowering the physics precision but this makes many levels simply unplayable as bodies intersect one another and collapse in on themselves.

So my question is, is this a lost cause or is there anything I can do to beef up performance?

Answer 1

First of all, love your game on Windows Phone 7!

Secondly, I don't see anything out of the ordinary in your profiler output. I did a quick and dirty performance analysis of the Farseer engine once (running in .net) and came up with similar results. It almost looks like you have a slowdown that is proportional across the board and may be due to mono itself.