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I have a system that should receive an interrupt from a digital I/O card at 10Hz. Every so often the CPU usage will ramp up to about 60%. When I examine /proc/interrupts the count for interrupt associated with the digital I/O card is increasing at a rate of ~30K interrupts/sec.

Does the interrupt count in /proc/interrupts,

  1. get incremented once an interrupt has been received by the IO-APIC?
  2. by the digital I/O card driver?
  3. something else?

To put it another way, when the count in /proc/interrupts is incrementing excessively is it because the system is actually receiving 30K intr/s (ie faulty hardware) or could this be caused by a buggy driver?

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