Re: [libvirt] [PATCH v3 1/3] qemu: Use virtio-pci by default for mach-virt guests
On Tue, 2017-01-10 at 03:38 -0500, Laine Stump wrote:
[...]
> - if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_VIRTIO_MMIO))
{
> - qemuDomainPrimeVirtioDeviceAddresses(
> - def, VIR_DOMAIN_DEVICE_ADDRESS_TYPE_VIRTIO_MMIO);
> + /* We use virtio-mmio by default on mach-virt guests only if they already
> + * have at least one virtio-mmio device: in all other cases, we prefer
> + * virtio-pci */
> + if (qemuDomainMachineHasPCIeRoot(def) &&
> + !qemuDomainHasVirtioMMIODevices(def)) {
> + qemuDomainPrimeVirtioDeviceAddresses(def,
> + VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI);
I'm having trouble remembering, and it's too early in the morning to go
looking in the code - it seems like priming the addresses with PCI might
not be necessary - as long as we simply *don't* prime them with
virtio-mmio. I could be misremembering though. ACK either way.
It looks like that's indeed the case from changing the code
accordingly and running the test suite.
However, a cursory look (it's morning here as well ;) at the
code didn't give me enough confidence that it's working by
design rather than pure chance, and with the freeze coming
up shortly I decided to push the possibly slightly suboptimal
code instead. I will go back to this and remove it if it
turns out to be safe to do so after 3.0.0 is out.
(ACK is based on the assumption that all concerned ARM parties have
agreed that it's time to do this. I *think* that is the case :-)
It's been agreed a while ago that the only thing stopping us
from changing the default was poor guest support; as mentioned
in the commit message, that's no longer a concern, so onwards
to the future we go! :)
Thanks for the review.
--
Andrea Bolognani / Red Hat / Virtualization