Subject: PMAC 11.2 (G5 QUAD) spurious IRQ issues

From: Peter Saisanas <[email-masked]>
Date: Wed, 23 Dec 2015 16:27:04 +1100

Hi,
Regarding the Powermac G5 Quad (PMAC 11.2), i have compiled a few 
different kernels and they all seem to generate spurious interrupts.
Observing the output of cat /proc/interrupts, it seems that each 
individual IRQ number assigned for most devices has the interrupt 
serviced by all 4 CPU cores simultaneously.

When this occurs, the spurious interrupt count increments for each core 
simultaneously.

However, if the irqbalance daemon is installed, the spurious interrupt 
counter doesn't increment anymore and irq's are distributed across each 
of the CPU's.

I have used various vanilla mainline kernels between 3.18.16 all the way 
to 4.4.0-rc5 and i seem to observe the same behavior.
Just wondering if anyone else has noticed this or am i configuring 
something wrong in the kernel?
No obvious side effect, however it just seemed like a strange observation.

Attached is my kernel config for 4.4.0-rc5.

Cheers,
Peter