We have derived that a packet can be handled in 11.5 
s,
and that an interrupt is serviced in 32.5 s. Therefore,
we can calculate the interrupt overhead for an interrupt that
services one packet: 32.5 - 11.5 = 21 s. The interrupt
overhead is caused by context switching. On interrupt handler entry,
the context of the current process and its thread must be saved. On
exit, it must be restored. Another negative effect of context
switching is cache usage. On handler entry, memory locations
different from the memory locations in the cache are used, and
therefore cache updates are required. In a similar way, the
interrupted process suffers from the interrupt: the cache it was
using is disturbed, and cache updates are required.