[RFC] ARM: Let GIC to route IRQs to any allowed CPUs

[Russell King - ARM Linux]

On Wed, Jan 12, 2011 at 04:18:51PM +0800, TAO HU wrote:
> The current logic will always route IRQs to the first allowed CPU
> Following two commands have the same result (all IRQs to CPU0)
> cmd1: $ echo 3 > proc/irq/xxx/smp_affinity
> cmd2: $ echo 1 > proc/irq/xxx/smp_affinity
> While below command will route all IRQs to CPU1
> cmd3: $ echo 2 > proc/irq/xxx/smp_affinity
> 
> With this patch, cmd1 will route IRQs to both CPU0 and CPU1
> Meanwhile, cmd2 and cmd3 will work as before

There's a reason we don't do this...

We don't want to deliver one IRQ to both CPU0 and CPU1 at the same time,
which is what will happen with this patch.  The GIC hardware doesn't
do IRQ balancing between CPUs.

The result will be CPUs fighting over servicing such interrupts.