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Interrupt overhead

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.



Marcel Boosten
Wed Mar 11 14:25:07 MET 1998