Re: excessive interrupts on network cards

Andrew Morton (
Tue, 25 Sep 2001 13:01:53 -0700

Chris Newton wrote:
> Hi,
> I 'think' the number of interrupts being generated for the network traffic I
> monitor, is excessive. Having talked quikly with Donald Becker, he indicated
> that I should be seeing a little less than the number of RX/TX packets/s on a
> wire, in terms of interrupts/s. That, however, is not what I am seeing. I am
> seeing 3 times as many interrupts/s as I am seeing packets/s.
> I have used three network devices to look at the stream I am monitoring, and
> it is usually aorund 5K packet/s IN, and 5K out, fed full duplex into a single
> 3Com 3c982 (2.4.10 kernel reports that anyways). However, watching:

3c982 is a dual-port server NIC. Is your card dual-port? If not, it's probably
a 3c980, and I goofed :)

> 'procinfo -D', reports on the order of 30,000 interrupts per second.

That does sound rather high. You should compare the interrupt rate
with the packet rate from `ifconfig' or /proc/net/dev.

Normally, 3c59x will show approx three Tx packets per interrupt
and one Rx packet per interrupt. It varies with workload, but
it tends to vary in the "good" direction - at higher packet
rates, we do more work in a single interrupt and the interrupt-per-packet
rate falls.
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