Re: [PATCH 07/14] genirq: Add a new generic IPI reservation code to irq core

Thomas Gleixner
2015-11-16T15:10:16Z

On Mon, 9 Nov 2015, Qais Yousef wrote:
> On 11/07/2015 01:31 PM, Thomas Gleixner wrote:
> > On Tue, 3 Nov 2015, Qais Yousef wrote:
> > > +
> > > + /* always allocate a virq per cpu */
> > > + nr_irqs = ipi_mask_weight(dest);
> > That's not really a good assumption. Not all architectures need
> > seperate interrupt numbers / descriptors because they can allocate
> > from a per cpu interrupt space. We really want to handle that here as
> > well. So we need a flag in the IPI domain which tells us whether that
> > allocation needs to be weight(desc) or 1.
>
> OK. But is it bad to always allocate the weight? I thought allocating virqs is
> cheap, or maybe not?

It's wrong to allocate the descriptors in the case of per cpu
interrupts. Aside of wasting memory its not representing what the
hardware does.

Thanks,

tglx