Re: [Qemu-ppc] [Qemu-devel] [PATCH V7 15/16] virtio-pci: increase the maximum number of virtqueues to 513

[Eduardo Habkost]

On Thu, Apr 23, 2015 at 02:21:48PM +0800, Jason Wang wrote:
> This patch increases the maximum number of virtqueues for pci from 64
> to 513. This will allow booting a virtio-net-pci device with 256 queue
> pairs on recent Linux host (which supports up to 256 tuntap queue pairs).
> 
> To keep migration compatibility, 64 was kept for legacy machine
> types. This is because qemu in fact allows guest to probe the limit of
> virtqueues through trying to set queue_sel. So for legacy machine
> type, we should make sure setting queue_sel to more than 63 won't
> make effect.
> 
> Cc: Paolo Bonzini <address@hidden>
> Cc: Richard Henderson <address@hidden>
> Cc: Michael S. Tsirkin <address@hidden>
> Cc: Alexander Graf <address@hidden>
> Cc: address@hidden
> Signed-off-by: Jason Wang <address@hidden>
> ---
>  hw/i386/pc_piix.c      | 5 +++++
>  hw/i386/pc_q35.c       | 5 +++++
>  hw/ppc/spapr.c         | 5 +++++
>  hw/virtio/virtio-pci.c | 6 +++++-
>  4 files changed, 20 insertions(+), 1 deletion(-)
> 
[...]
>  static void pc_compat_2_3(MachineState *machine)
>  {
> +    ObjectClass *klass = object_class_by_name("virtio-pci-bus");
> +    VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);
> +
> +    k->queue_max = 64;
>  }
[...]
>  static void pc_compat_2_3(MachineState *machine)
>  {
> +    ObjectClass *klass = object_class_by_name("virtio-pci-bus");
> +    VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);
> +
> +    k->queue_max = 64;
>  }
[...]
>  static void spapr_compat_2_3(Object *obj)
>  {
> +    ObjectClass *klass = object_class_by_name("virtio-pci-bus");
> +    VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);
> +
> +    k->queue_max = 64;
>  }

If you use compat_props for this, you will just need to add it to
HW_COMPAT_2_3 without duplicating the same compat code on all machines.

-- 
Eduardo