Re: [PATCH] irq: Add node_affinity CPU masks for smarter irqbalance hints

[Yong Zhang <yong.zhang0@gmail.com>]

[snip]
>>
>> 1) I think you should consider CONFIG_CPUMASK_OFFSTACK which will affect
>>    node_affinity.
>> 2) It seems like this patch can't work with SPARSE_IRQ.
>
> This mechanism isn't going to be used by any internal kernel mechanism
> for determining interrupt placement or operation.  It's purely something
> that either a driver can modify, or external script (through /proc),
> that irqbalance will make use of.  If irqbalance isn't running, or the
> current version of irqbalance doesn't support reading node_affinity,
> then it won't affect the system's operation.
>
> If irqbalance does support it, it'll read whatever the supplied mask is,
> and then will try and balance interrupts within that mask.  It will bail
> if the mask is invalid, or won't apply to the running system, just like
> how putting a bogus mask into smp_affinity is ignored.
>
> If there's something I'm missing beyond this with the two suggestions
> you've made (I looked into those two parameters and tried to draw
> conclusions), please let me know.

My two suggestions are both about your adding node_affinity. Before you can
use this element, you must initialise it firstly. You can refer how
irq_desc::affinity
is used in function alloc_desc_masks().
include/linux/irq.h:
static inline bool alloc_desc_masks(struct irq_desc *desc, int node,
							bool boot)
{
	gfp_t gfp = GFP_ATOMIC;

	if (boot)
		gfp = GFP_NOWAIT;

#ifdef CONFIG_CPUMASK_OFFSTACK
	if (!alloc_cpumask_var_node(&desc->affinity, gfp, node))
		return false;

#ifdef CONFIG_GENERIC_PENDING_IRQ
	if (!alloc_cpumask_var_node(&desc->pending_mask, gfp, node)) {
		free_cpumask_var(desc->affinity);
		return false;
	}
#endif
#endif
	return true;
}

Thanks,
Yong

>
> Cheers,
> -PJ Waskiewicz
>
>