> Virtual dispatch absolutely has an overhead, but absolutely nobody in their right mind should be using COM interfaces in a critical section of code.

I could definitely be wrong, but I think C++ style "virtual dispatch" (ie, following two pointers instead of one to get to your function) doesn't really cost anything anymore, except for the extra pointers taking up cache space.

Don't all of the Windows DirectX gaming interfaces use COM? And isn't AAA gaming performance critical?

> Don't all of the Windows DirectX gaming interfaces use COM? And isn't AAA gaming performance critical?

Yes, on both counts. You will also, on average, be making fewer calls to ID3D12CommandQueue methods than one would think - you'd submit an entire vertex buffer for a model (or specific components of it that need the same pipeline state, at least) at once, allocate larger pools of memory on the GPU and directly write textures to it, etc.

This is the entire design behind D3D12, Vulkan, and Metal - more direct interaction with the GPU, batching submission, and caching command buffers for reuse.

When I'm talking about "critical sections" of code, I mean anything with a tight loop where you can reasonably expect to pin a CPU core with work. For a game, this would be things like creating vertex buffers, which is why all three major API's take these as bare pointers to data structures in memory instead of requiring discrete calls to create and populate them.