x86_64 IOAPIC

[SUJIT V <sujit.linux@gmail.com>]

Hi,
    We have a IBM Qauadcore 8 CPU system running x86_64 linux 2.6.23.
We were doing some performance test. (disk & network).
The eth0 IRQ is pinned to CPU0.  The aacraid interrupt has not been
assigned any smp affinity.

On the system we see in (/proc/interrupts) that when the eth0
interrupt rate is high, the aacraid interrupt counter for CPU0 does
not increase as much compared to aacraid interrupts handled by other
CPUs .
This shows that IOAPIC is doing some load balancing.

I wanted to check the code which is doing this load balancing. I
checked the file arch/x86_64/kernel/io_apic.c. I could not find any
irq balancing stuff out there.
I went through some archived discussions about the x86_64 ioapic irq
balancing. Most of the discussions were about using irqbalance
utility.


Could some one point me to the relevant piece of io_apic code ?


Thanks