Re: [RFC Part2 v1 02/21] genirq: Introduce helper functions to support stacked irq_chip

Thomas Gleixner
2014-09-17T20:59:54Z

On Wed, 17 Sep 2014, Jiang Liu wrote:
> On 2014/9/17 1:45, Thomas Gleixner wrote:
> > On Thu, 11 Sep 2014, Jiang Liu wrote:
> >> +#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
> >> +void irq_chip_ack_parent(struct irq_data *data)
> >> +{
> >> + data = data->parent_data;
> >> + if (data && data->chip && data->chip->irq_ack)
> >> + data->chip->irq_ack(data);
> >
> > Why is this restricted to a single parent level and does not go down
> > the whole stack?
> Hi Thomas,
> It happens to work on x86, and we want to achieve a bit
> performance advantage by not walking down the whole stack.
> If preferred, I will change it to walk the whole stack.

Happens to work on my machine is always a bad argument :)

Now, I can see why you want to do that, but if we do an optimization
like that then we should really get rid of the conditional.

You surely need a conditional on data->chip and data->chip->callback
for a full stackq walk, but for an explicit request to use the parents
ack the parent better has a chip with an ack function, right?

void irq_chip_ack_parent(struct irq_data *data)
{
data = data->parent_data;
data->chip->irq_ack(data);
}

Thanks,

tglx