Re: [PATCH 0/7] Enable vdpa net migration with features depending on CVQ

[Jason Wang <jasowang@redhat.com>]

On Sat, Jul 29, 2023 at 1:20 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> At this moment the migration of net features that depends on CVQ is not
> possible, as there is no reliable way to restore the device state like mac
> address, number of enabled queues, etc to the destination.  This is mainly
> caused because the device must only read CVQ, and process all the commands
> before resuming the dataplane.
>
> This series lift that requirement, sending the VHOST_VDPA_SET_VRING_ENABLE
> ioctl for dataplane vqs only after the device has processed all commands.

I think it's better to explain (that is what I don't understand) why
we can not simply reorder vhost_net_start_one() in vhost_net_start()?

    for (i = 0; i < nvhosts; i++) {
        if (i < data_queue_pairs) {
            peer = qemu_get_peer(ncs, i);
        } else {
            peer = qemu_get_peer(ncs, n->max_queue_pairs);
        }

        if (peer->vring_enable) {
            /* restore vring enable state */
            r = vhost_set_vring_enable(peer, peer->vring_enable);

            if (r < 0) {
                goto err_start;
            }
        }

=>      r = vhost_net_start_one(get_vhost_net(peer), dev);
        if (r < 0) {
            goto err_start;
        }
    }

Can we simply start cvq first here?

Thanks

> ---
> From FRC:
> * Enable vqs early in case CVQ cannot be shadowed.
>
> Eugenio Pérez (7):
>   vdpa: export vhost_vdpa_set_vring_ready
>   vdpa: add should_enable op
>   vdpa: use virtio_ops->should_enable at vhost_vdpa_set_vrings_ready
>   vdpa: add stub vhost_vdpa_should_enable
>   vdpa: delay enable of data vqs
>   vdpa: enable cvq svq if data vq are shadowed
>   vdpa: remove net cvq migration blocker
>
>  include/hw/virtio/vhost-vdpa.h |  9 +++++
>  hw/virtio/vhost-vdpa.c         | 33 ++++++++++++----
>  net/vhost-vdpa.c               | 69 ++++++++++++++++++++++++++--------
>  hw/virtio/trace-events         |  2 +-
>  4 files changed, 89 insertions(+), 24 deletions(-)
>
> --
> 2.39.3
>
>