NIC Interrupts on Multi-Core

I wonder how many people out there have this issue and don't even know it. Let me explain what happening and how you would detect the problem and then suggest some ways to go about fixing it.

The easiest way to go about seeing if you have the problem is to cat the /proc/interrupts file.

[blog@web ~]$ cat /proc/interrupts
           CPU0       CPU1       CPU2       CPU3
  0:  165886477          0          0          0    IO-APIC-edge  timer
  1:          3          0          0          0    IO-APIC-edge  i8042
  8:          0          0          0          0    IO-APIC-edge  rtc
  9:          0          0          0          0   IO-APIC-level  acpi
 12:          4          0          0          0    IO-APIC-edge  i8042
 50:          0          0          0          0   IO-APIC-level  sata_nv
 58:          0          0          0          0   IO-APIC-level  sata_nv
 82:        210          0          0     107566         PCI-MSI  eth0
 90:         49          0     100834          0         PCI-MSI  eth1

So you are asking now what are you to be looking for, well check out the eth0 and eth1 lines. As you can see this is a 4 Core box and has all the interrupts for eth0 running on CPU3 and eth1 on CPU2. This box is not in production so the numbers are small but still shows a problem. Following post will suggest fixes to this problem and the fix that I took.