Bug Burst & Generics speed

Hi all, I've discovered something interesting. The basic code is here:

Code (CSharp):

1. public struct Util<T> where T : struct, INativeList<MyStruct>
2. {
3.     public static void Eval_Generic(in T list) { //evaluate }
4.     public static void Eval_Fixed(in FixedList4096<MyStruct> list) { // evaluate }
5. }

What I've discovered is that the

Eval_Generic

runs about 5x slower, despite the function signature being the same in the Burst Inspector.

I am wondering if this is supposed to be so, and if there's a way to get the generic version to run as fast as the native one.

 

I have also realized this may not be a Burst thing, it could come down to the IL emitted by the compiler.

 

One possible cause could be the interaction between non readonly struct and in parameters. Basically the larger the struct you are passing the slower it gets due to defensive copying that can't be optimized as much when using generics. That should be visible in the burst inspector on the caller side of things though.

The other thing I have seen (though not in burst) is that due to the INativeList<> constraint it sometimes doesn't optimize out the boxing of the struct.

 

I did not know about the performance penalty for

in

parameters. I changed them all to

ref

and it's fixed the problem completely. TMYK I guess