Re: [PATCH] Move irq sharing information to irqchip level.

[Gleb Natapov <gleb@redhat.com>]

On Sun, Aug 23, 2009 at 02:46:38PM +0300, Avi Kivity wrote:
> On 08/23/2009 02:36 PM, Gleb Natapov wrote:
> >>>
> >>>The problem is that at this level it is not known if GSI is MSI or not.
> >>>Current code dials with this by arbitrary assuming that GSI is MSI if it
> >>>is greater then KVM_IOAPIC_NUM_PINS, but this is not enforced when
> >>>routing table is installed and userspace is free to use any GSI as MSI.
> >>>Of cause this problem would not exist if MSIs were not linked to GSIs
> >>>in the first place.
> >>Does msi actually care about the states?  I don't think it does.
> >>
> >That is the point. MSI doesn't care, but we don't know if GSI is MSI or
> >not.
> 
> So we toggle the bits needlessly.  Just like with edge-triggered interrupts.
If we can avoid it why not?

> >>No, it's more correct at the GSI level, since all interrupt lines
> >>connected to one GSI are shared.
> >>
> >Why? All interrupts connected to the same irqchip pin (through pci irq
> >router or other onboard logic) are shared. GSI is pure logical
> >abstraction.
> 
> All interrupts connected through one GSI are shared, so why not keep
> the level information shared as well?
> 
If we will keep sharing info at irq routing table level how will we recalculate
sharing state when irq routing table changes?

--
			Gleb.