Total Interrupt Time is the average percentage of time that all processors spend receiving and servicing hardware interrupts ...

% Total Interrupt Time is the average percentage of time that all processors spend receiving and servicing hardware interrupts during sample intervals, where the value is an indirect indicator of the activity of devices that generate interrupts. It is the sum of Processor: % Interrupt Time for of all processors on the computer, divided by the number of processors.  DPCs are counted separately and are not a component of the interrupt count.  This value is an indirect indicator of the activity of devices that generate interrupts, such as the system timer, the mouse, disk drivers, data communication lines, network interface cards and other peripheral devices.