Hello list, I was advised to post this question by Jesse Barnes; I also
posted to KVM list.
I am running Ubuntu-Precise 3.2.0-29-generic #46, with stock KVM ("QEMU
emulator version 1.0 (qemu-kvm-1.0)") on a Dell R510 server. I have one
dual-port Intel's NIC 82599, of which I spawn 32 VFs from each port. I spawn
virtual machines with KVM, each VM has 4 VFs attached (two from each PF).
Once in a while, in particular when I spawn multiple VMs in parallel, I hit
an issue that one of the VFs does not have an IRQ assigned to it. I am
checking this in /proc/interrupts, looking for entries like
"kvm:0000:03:14.6". In some cases, an entry is missing for a particular VF.
As a result, the VF within the VM is non-functional.
I debugged this issue further, by adding prints to kvm.ko code. I see that
the failure happens in kvm_vm_ioctl_assigned_device/KVM_ASSIGN_DEV_IRQ path,
which calls assigned_device_enable_host_msix() function, which calls
pci_enable_msix(), which fails with EINVAL or with ENOMEM. This path is
called twice for each VF.
I see that first pci_enable_msix() returns -12/-22, and when
kvm_vm_ioctl_set_msix_nr() is called again, it sees that adev->entries_nr !=
0 and fails the call with EINVAL. I can repro it only when spawning like 8
or 10 VMs in parallel, but it doesn't happen every time. So it seems like
this is not a resource shortage problem, but some race somewhere.
I tested this with several version of ixgbe drivers, including the in-tree
version that comes with Precise. It reproduces with all the versions.
Can anybody pls advise on how to debug this issue further?
Thanks,
Alex.
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