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From:   Jason Wang <jasowang@redhat.com>
Date:   Mon, 17 Oct 2022 15:08:19 +0800
Message-ID: <CACGkMEvaKnqS-0p7iqyHP_Wbbj1YdmPFA7ABfKK_8FbXMsZEkg@mail.gmail.com>
Subject: Re: [PATCH 0/4] vDPA: dev config export via "vdpa dev show" command
To:     Si-Wei Liu <si-wei.liu@oracle.com>
Cc:     mst@redhat.com, virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, Sean Mooney <smooney@redhat.com>,
        Daniel Berrange <berrange@redhat.com>
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Adding Sean and Daniel for more thoughts.

On Sat, Oct 15, 2022 at 9:33 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
> Live migration of vdpa would typically require re-instate vdpa
> device with an idential set of configs on the destination node,
> same way as how source node created the device in the first place.
>
> In order to allow live migration orchestration software to export the
> initial set of vdpa attributes with which the device was created, it
> will be useful if the vdpa tool can report the config on demand with
> simple query.

For live migration, I think the management layer should have this
knowledge and they can communicate directly without bothering the vdpa
tool on the source. If I was not wrong this is the way libvirt is
doing now.

> This will ease the orchestration software implementation
> so that it doesn't have to keep track of vdpa config change, or have
> to persist vdpa attributes across failure and recovery, in fear of
> being killed due to accidental software error.
>
> In this series, the initial device config for vdpa creation will be
> exported via the "vdpa dev show" command.
> This is unlike the "vdpa
> dev config show" command that usually goes with the live value in
> the device config space, which is not reliable subject to the dynamics
> of feature negotiation and possible change in device config space.
>
> Examples:
>
> 1) Create vDPA by default without any config attribute
>
> $ vdpa dev add mgmtdev pci/0000:41:04.2 name vdpa0
> $ vdpa dev show vdpa0
> vdpa0: type network mgmtdev pci/0000:41:04.2 vendor_id 5555 max_vqs 9 max_vq_size 256
> $ vdpa dev -jp show vdpa0
> {
>     "dev": {
>         "vdpa0": {
>             "type": "network",
>             "mgmtdev": "pci/0000:41:04.2",
>             "vendor_id": 5555,
>             "max_vqs": 9,
>             "max_vq_size": 256,
>         }
>     }
> }
>
> 2) Create vDPA with config attribute(s) specified
>
> $ vdpa dev add mgmtdev pci/0000:41:04.2 name vdpa0 \
>     mac e4:11:c6:d3:45:f0 max_vq_pairs 4
> $ vdpa dev show
> vdpa0: type network mgmtdev pci/0000:41:04.2 vendor_id 5555 max_vqs 9 max_vq_size 256
>   mac e4:11:c6:d3:45:f0 max_vq_pairs 4
> $ vdpa dev -jp show
> {
>     "dev": {
>         "vdpa0": {
>             "type": "network",
>             "mgmtdev": "pci/0000:41:04.2",

So "mgmtdev" looks not necessary for live migration.

Thanks

>             "vendor_id": 5555,
>             "max_vqs": 9,
>             "max_vq_size": 256,
>             "mac": "e4:11:c6:d3:45:f0",
>             "max_vq_pairs": 4
>         }
>     }
> }
>
> ---
>
> Si-Wei Liu (4):
>   vdpa: save vdpa_dev_set_config in struct vdpa_device
>   vdpa: pass initial config to _vdpa_register_device()
>   vdpa: show dev config as-is in "vdpa dev show" output
>   vdpa: fix improper error message when adding vdpa dev
>
>  drivers/vdpa/ifcvf/ifcvf_main.c      |  2 +-
>  drivers/vdpa/mlx5/net/mlx5_vnet.c    |  2 +-
>  drivers/vdpa/vdpa.c                  | 63 +++++++++++++++++++++++++++++++++---
>  drivers/vdpa/vdpa_sim/vdpa_sim_blk.c |  2 +-
>  drivers/vdpa/vdpa_sim/vdpa_sim_net.c |  2 +-
>  drivers/vdpa/vdpa_user/vduse_dev.c   |  2 +-
>  drivers/vdpa/virtio_pci/vp_vdpa.c    |  3 +-
>  include/linux/vdpa.h                 | 26 ++++++++-------
>  8 files changed, 80 insertions(+), 22 deletions(-)
>
> --
> 1.8.3.1
>