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Subjectexcessive interrupts on network cards
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:

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

This page:

http://www.scyld.com/network/3c509.html

has a snipet:

"some other device or device driver hogging the bus or disabling interrupts.
Check /proc/interrupts for excessive interrupt counts. The timer tick
interrupt should always be incrementing faster than the others. "

Well, looking at this machine, since it booted 57 minutes ago:


[root@phantom /proc]# more interrupts
CPU0 CPU1
0: 172754 171041 IO-APIC-edge timer
1: 0 3 IO-APIC-edge keyboard
2: 0 0 XT-PIC cascade
14: 2 2 IO-APIC-edge ide0
16: 87361 87539 IO-APIC-level eth2
20: 6798697 6799977 IO-APIC-level eth0
21: 0 0 IO-APIC-level eth1
30: 11837 11806 IO-APIC-level aic7xxx
31: 199418 199209 IO-APIC-level aic7xxx
NMI: 0 0
LOC: 343669 343708
ERR: 0
MIS: 0


In 57 minutes, that ethernet card has generated: 14,000,459 interrupts.

Isn't this excessive?

I also have a different brand card on board... an intel ether express pro.
So... I swapped the cables so that the intel card would see that network
stream. Well, it caused even more interrupts per second. (more like 40K).


I have tried kernel 2.4.9, 2.4.2 (redhat 7.1 version), and just now, 2.4.10,
all SMP builds, on a dual 1 GHz PIII, with 1 GB of SDRAM, Adaptec 7899
Ultra160 controller, two 3c982 netcards and one onboard intel etherexpress pro
100 cards.

Guess my question is, first of.. is this normal?

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