what is mean of "microcode instructions"?

Accelerated Computing CUDA CUDA Programming and Performance
1

hi
i read this expression in appendix.A of cuda programming guide 2.3.1 :
“The limit on kernel size is 2 millions of microcode instructions”
i dont now mean of “microcode instructions”.
who can tell me what this meaning?

2

You can read about it here:
Microcode
I have kernels with hunderts of code lines and it works without problems.