On Mon, Mar 12, 2012 at 05:44:00PM +0800, Jason Wang wrote: > On 03/12/2012 05:23 PM, Gleb Natapov wrote: > >On Mon, Mar 12, 2012 at 05:07:35PM +0800, Jason Wang wrote: > >>> Currently, we call ioapic_service() immediately when we find the irq is still > >>> active during eoi broadcast. But for real hardware, there's some dealy between > >>> the EOI writing and irq delivery (system bus latency?). So we need to emulate > >>> this behavior. Otherwise, for a guest who haven't register a proper irq handler > >>> , it would stay in the interrupt routine as this irq would be re-injected > >>> immediately after guest enables interrupt. This would lead guest can't move > >>> forward and may miss the possibility to get proper irq handler registered (one > >>> example is windows guest resuming from hibernation). > >>> > >Yes, I saw this behaviour with Windows NICs, but it looks like the > >guest bug. Does this happen with other kind of devices too? Because > >if it does not then the correct hack would be to add a delay between > >Windows enabling PHY and sending first interrupt to a guest. This will > >model what happens on real HW. NIC does not start receiving packets at > >the same moment PHY is enabled. Some time is spent bring up the link. > > > > Looks common for any unhandled level irq but I haven't tried. What > I've tested is running a similar test program by hacking the card > driver and let it run in both real physical machine and a kvm guest, > and see what happens if there's no irq handled: > > - In real hardware, there's a gap between two successive irqs > injected by eoi broadcast, and OS can move forward. > - In a kvm guest, no gap, guest can't move forward and would always > stay in the irq context forever. This is not something an OS should rely on. So lets do the Windows hack in QEMU NIC devices. -- 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
