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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Mar 21, 2011 at 09:10:32PM +0900, Isaku Yamahata wrote:
> 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.

I expect it won't change the behaviour because the interrupts
are level: at the moment e.g. pci devices already reassert
interrupts on load.

But I agree it better be a separate patch, and needs a lot of testing.

> -- 
> yamahata