I think you should know at least one level of abstraction, in each direction, beyond what you presently know. So if you're writing a C driver, you should know w

I think you should know at least one level of abstraction, in each direction, beyond what you presently know. So if you're writing a C driver, you should know what the assembly will look like and also what the application developer will be writing with the help of your driver. This probably has more to do with communication and understanding of the people problems involved than with performance though.