Performance of C# using C++ wrapped libraries

Question

I have read this and this and was wondering if I use in C# functions from unmanaged C++ library via C# wrapper of this library, is there going to be any difference in performance compared with the same program, but written fully with unmanaged C++ and the C++ library? I am asking about crucial performance difference bigger then 1.5 times. Notice I am asking about the function performance of the C++ library only(in the two ways - with and without the use of C# wrapper), isolating the other code!

After edit:

I was just wondering if I want to use C++ dynamic unmanaged library(.dll) in C# and I am using wrapper - which is going to be compiled to intermediate CIL code and which is not. I guess only the wrapper is being compiled to CIL, and when C# want to use C++ function from the library it is just parsing and passing the arguments to C++ function with the use of the wrapper, so there will be maybe some delay, but not like if I write the whole library via C#. Correct me if I am mistaking please.

Answer 1

Of course, there is overhead involved in switching from managed to unmanaged code execution. It is very modest, takes about 12 cpu cycles. All that needs to be done is write a "cookie" on the stack so that the garbage collector can recognize that subsequent stack frames belong to unmanaged code and therefore should not be inspected for valid object references.

These cookies are strung together like a linked-list, supporting the scenario where C# code calls native code which in turn calls back into managed code. Traversed by the GC when it collects. Not as uncommon as it sounds, it happens in any GUI app for example. The Click event is a good example, triggered when the UI thread pinvokes GetMessage().

Not the only thing that needs to happen however, in any practical scenario you also pass arguments to the native function. They can require a lot more work to get marshaled into a format that the native code can understand. Arrays in particular, they'll need to get pinned if the array elements are blittable , that's still pretty cheap. Gets expensive when the entire array needs to be converted because the element is not blittable. Not always easy to recognize, a profiler is forever the proper tool to detect inefficient code.