Is "top" accounting for Kernel Interrupts?

I have a simple interrupt that is triggered by a GPIO-input. The IRQ only increments a variable and returns. When I turn the frequency of the interrupts up to somewhere around 10-20 kHz, the system becomes unresponsive. I measure the CPU-load using top while turning the frequency up, but there is no significant change in any of the metrics from the top command. So the processor CPU gets loaded, but I can't measure it with top! How is top making its measurement? How come the very frequent interrupt isn't visible? **How can I measure the impact the interrupt has on the overall performance of the system?** **EDIT** By setting the CPU-frequency governor to "performance", and setting the frequency to static 1GHz, I was able to get the interrupt frequency up to 150kHz, before the processor crashed..