Re: [libvirt] [Qemu-devel] [PATCH v4] Add machine parameter qemu-kvm-migration for live migrate compatibility with qemu-kvm
Markus,
On 24 Sep 2014, at 09:05, Markus Armbruster <armbru(a)redhat.com> wrote:
Alex Bligh <alex(a)alex.org.uk> writes:
> This patch series adds inbound migrate capability from qemu-kvm version
> 1.0. The main ideas are those set out in Cole Robinson's patch here:
>
http://pkgs.fedoraproject.org/cgit/qemu.git/tree/0001-Fix-migration-from-...
> however, rather than patching statically (and breaking inbound
> migration on existing machine types), I have added a new machine
> parameter (qemu-kvm-migration) which when turned on affects the pc-1.0
> machine type. Usage:
> -machine pc-1.0,qemu-kvm-migration=on
Forgive me if this has been discussed already: why not simply a separate
machine type "pc-1.0-qemu-kvm"?
That's what v2 of the patch set does (and I prefer v2). However, mst
wanted it done this way.
> Three aproaches are taken:
>
> * cirrus-vga.vgamem_mb defaults to 16 rather than 8. In order to
> keep -global cirrus-vga.vgamem_mb working even with
> qemu-kvm-migration=on, this is monkey-patched into the default
> value of the MachineState structure's compat_props list.
This part fires only for pc-1.0, because it's in
pc_early_init_pci_1_0().
Yes, intentional. I should have noted that. That's because
qemu-kvm-migration=on the VRAM change was designed to
work only with pc-1.0. I haven't looked at trying to make
other (older) qemu-kvm machine migrations work, but (with the stuff
below), I would guess it would work with the appropriate
command line options for VRAM size.
Obviously I could put early init elsewhere.
> * In hw/timer/i8254_common.c, the VMSTATE_UINT32_TEST macro
> is used to test the version for the irq_disable flags,
> allowing version 3 or more, or version 2 for an inbound
> migrate from qemu-kvm (only).
>
> * In hw/acpi/piix4.c, qemu-kvm incorrectly uses version 2 for
> a version 3 structure, causing acpi_load_old to be used.
> acpi_load_old detects this situation based on the machine type
> and restarts the attempt to load the vmstate using a
> customised VMStateDescription. The above cleaner approach is
> unavailable here.
These parts apply to all machine types, don't they?
They apply only when qemu-kvm-migration=on is selected, but to
any machine type; however machine types newer than pc-1.0 will
be exporting v3 I think anyway.
> Changes since v1:
> * Do not use a machine type, use a machine parameter.
Okay, it has been discussed already. I'd appreciate a brief recap all
the same.
See above. I preferred the machine type. But I got to learn more about
QOM on the way :-)
--
Alex Bligh