Messages in this thread | | | Date | Mon, 12 Mar 2012 17:44:00 +0800 | From | Jason Wang <> | Subject | Re: [PATCH] kvm: ioapic: conditionally delay irq delivery during eoi broadcast |
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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.
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