excessive interrupts on network cards

From: Chris Newton (newton@unb.ca)
Date: Tue Sep 25 2001 - 14:20:17 EST


  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:


  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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This archive was generated by hypermail 2b29 : Sun Sep 30 2001 - 21:00:33 EST