On Thu, Sep 16, 2010 at 03:38:28PM +0200, Michael S. Tsirkin wrote: > On Thu, Sep 16, 2010 at 03:14:11PM +0200, Avi Kivity wrote: > > On 09/16/2010 02:57 PM, Michael S. Tsirkin wrote: > > >> > > >> > > If you want to split parts that asserts irq and de-asserts it then we > > >> > > should have irqfd that tracks line status and knows interrupt line > > >> > > polarity. > > >> > > > >> > Yes, it can know about polarity even though I think it's cleaner to do this > > >> > per gsi. But it can not track line status as line is shared with > > >> > other devices. > > >> It should track only device's line status. > > > > > >There is no such thing as device's line status on real hardware, either. > > >Devices do not drive INT# high: they drive it low (all the time) > > >or do not drive it at all. > > > > > > > That's just an implementation detail. Devices either assert INT# or > > they do not. Tying the wires together constitutes an AND gate. > > This gate has to be modelled somewhere, currently it's in qemu's pci > > emulation. > > Right. kvm in kernel has this as well, we need to keep this in > kvm kernel if we want to support level with irqfd. > Where it does not belong is individual devices: these > should be able to assert INTx multiple times > and it should have no effect, as per spec. Assert_INTx/Deassert_INTx you mentioned are internal PCI thing. What KVM sees logically is status of the line between pci controller and irq chip. We do not emulate PCI inside kernel, but I agree that kernel should handle multiple asserts without de-assert in the middle and, in fact, it does. But the thread started with you trying to optimize this non-optimal device behaviour and I am saying that the fix should be elsewhere. Namely in irqfd. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
