On 04/11/2014 07:24 PM, Alexander Graf wrote: > > On 10.04.14 16:43, Alexey Kardashevskiy wrote: >> On 04/10/2014 11:26 PM, Alexander Graf wrote: >>> On 10.04.14 15:24, Alexey Kardashevskiy wrote: >>>> On 04/10/2014 10:51 PM, Alexander Graf wrote: >>>>> On 14.03.14 05:18, Alexey Kardashevskiy wrote: >>>>>> The current allocator returns IRQ numbers from a pool and does not >>>>>> support IRQs reuse in any form as it did not keep track of what it >>>>>> previously returned, it only had the last returned IRQ. >>>>>> However migration may change interrupts for devices depending on >>>>>> their order in the command line. >>>>> Wtf? Nonono, this sounds very bogus and wrong. Migration shouldn't change >>>>> anything. >>>> I put wrong commit message. By change I meant that the default state >>>> before >>>> the destination guest started accepting migration is different from what >>>> the destination guest became after migration finished. And migration >>>> cannot >>>> avoid changing this default state. >>> Ok, why is the IRQ configuration different? >> Because QEMU creates devices in the order as in the command line, and >> libvirt changes this order - the XML used to create the guest and the XML >> which is sends during migration are different. libvirt thinks it is ok >> while it keeps @reg property for (for example) spapr-vscsi devices but it >> is not because since the order is different, devices call IRQ allocator in >> different order and get different IRQs. > > So your patch migrates the current IRQ configuration, but once you restart > the virtual machine on the destination host it will have different IRQ > numbering again, right?
No, why? IRQs are assigned at init time from realize() callbacks (and survive reset) or as a part of ibm,change-msi rtas call which happens in the same order as it only depends on pci addresses and we do not change this either. > I'm not sure that's a good solution to the problem. I guess we should > rather aim to make sure that we can make IRQ allocation explicit. > Fundamentally the problem sounds very similar to the PCI slot allocation > which eventually got solved by libvirt specifying the slots manually. We can do that too. Who decides? :) -- Alexey
