[emn13]

I've got no numba experience whatsoever, but if you're doing real function calls and memory allocations for simple things like multiplying small matrices, your code will be at least an order of magnitude slower than optimal, even in C. malloc's a big hit, and function calls often are too - not just because of the call itself (and the CPU cache hit that can involve), but no less significantly because they're opaque to the optimizer - and that means that the wrapping function is often optimized much less well.

It's not a fundamental issue, but I haven't seen a JIT do this particularly well, yet. All that inlining makes compiling slower, so to some extent the run-time nature of the JIT is an inherent limitation here.