Linux Interrupts Issue

interruptslinux

Is there a simple way to determine if interrupts are a performance issue? I have the following from cat /proc/interrupts but really don't have a history of this server so I don't know if this could be causing any issues. I found the definition of each column at http://www.centos.org/docs/5/html/5.1/Deployment_Guide/s2-proc-interrupts.html but don't seem to find any guidelines on whether or not the results are acceptable.

       CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       CPU6       CPU7
 0: 1408788887          0          0          0          0          0          0          0    IO-APIC-edge  timer
 1:          3          0          0          0          0          0          0          0    IO-APIC-edge  i8042
 8:          1          0          0          0          0          0          0          0    IO-APIC-edge  rtc
 9:          0          0          0          0          0          0          0          0   IO-APIC-level  acpi
12:          4          0          0          0          0          0          0          0    IO-APIC-edge  i8042
14:        476   92736034  560949599   89233642          0          0          0          0    IO-APIC-edge  ide0
66:         81          0          0          0          0          0          0          0   IO-APIC-level  ehci_hcd:usb1, uhci_hcd:usb2, uhci_hcd:usb4
74:        153   62468419  147960075   25257462          0          0          0          0   IO-APIC-level  uhci_hcd:usb3, uhci_hcd:usb5
82: 1054378386          0          0          0          0          0          0          0         PCI-MSI  eth0
169:       8343 1516025027  954152248    6501060          0  757271678 1872714173    2565826   IO-APIC-level  megasas
NMI:   28336831   18526902   35866900   13915052   25165724   26928152   21827791   19303613
LOC: 1408788527 1408756844 1408788059 1408788084 1408788124 1408787843 1408787972 1408787711
ERR:          0
MIS:          0

Best Answer

The highest count of interrupts you have still averages to:

1872714173 interrupts / 83014987.85 seconds = 23 intr/s

which is not fearsome at all. As they are, these statistics are perfectly acceptable. A peak of 7500 intr/s is also acceptable on a busy system.

Whatever have led you to the conclusion that interrupts are a relevant metric, I would take a step back and reconsider. These are more often an effect of a problem (completely different problem) than a sole cause of problem. Only situation that comes to mind would be some rogue device on a bus.

If you have sar reports, look for some other metric that peaks at the time of poor performance (run queue? paging? disk I/O?) and re-start your analysis from there.

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