[Qemu-devel] Re: [PATCH v3 3/3] piix_pci: optimize set irq path

[Isaku Yamahata <yamahata@valinux.co.jp>]

On Mon, Mar 21, 2011 at 01:37:07PM +0200, Michael S. Tsirkin wrote:
> > +static int piix3_post_load(void *opaque, int version_id)
> > +{
> > +    PIIX3State *piix3 = opaque;
> > +    piix3_update_irq_levels(piix3);
> 
> Couldn't figure out why would we not want to
> propagate the interrupts here.
> Could you explain please?
> What happens if we do propagate them?
> Nothing bad, right?

I wanted to be just conservative.
If you are brave enough to change the behavior, I'm fine with propagating
interrupts.

If we propagate the interrupts, guest OS may see interrupts
unnecessarily/spuriously injected after load.
Probably such interrupts doesn't harm OSes, so there is nothing
bad in theory as you said.
On the other hand, I hesitated to change the existing behavior because
it would be very difficult to debug it and to test many OSes.
-- 
yamahata