hELP ON Interrupts/sec

HI all,
i have a packet driver which keeps receiving 64 byte packets every ms.
at the rate of 1000 packets/sec i am getting 2000 interrupts/sec. Why
is this so?? should it not be 1000 interrupts/sec rather then 2000.
Also when the rate of incoming packets increases then interrupts increases
proportionally ie
pkts/sec interrupts/sec
1000 2000
2000 4000
4000 8000

Is this a cause of concern??
can anybody tell me if this is normal or something
abnormal is happening here.