在 2021/8/19 上午1:33, Michael S. Tsirkin 写道:
On Wed, Aug 18, 2021 at 12:31:39PM +0800, Jason Wang wrote:
On Wed, Aug 18, 2021 at 11:15 AM Parav Pandit <parav@xxxxxxxxxx> wrote:
From: Michael S. Tsirkin <mst@xxxxxxxxxx>
Sent: Tuesday, August 17, 2021 2:24 AM
On Mon, Aug 09, 2021 at 09:51:49AM +0000, Parav Pandit wrote:
From: Michael S. Tsirkin <mst@xxxxxxxxxx>
Sent: Monday, August 9, 2021 3:10 PM
On Fri, Aug 06, 2021 at 08:55:56AM +0000, Parav Pandit wrote:
The point is to try and not reinvent a dedicated vpda interface
where a generic one exits.
E.g. for phy things such as mac speed etc, I think most people
are using ethtool things right?
As you know vdpa is the backend device for the front-end netdevice
accessed by the ethtool.
vdpa management tool here is composing the vdpa device.
For example creator (hypervisor) of the vdpa devices knows that a
guest VM is given 4 vcpus, So hypervisor creates a vdpa devices
with config space layout as, max_virtqueue_pairs = 4.
And the MAC address chosen by hypervisor in mac[6].
Guest VM ethtool can still chose to use less number of channels.
Typically,
ethtool is for guest VM.
vdpa device is in hypevisor.
How can hypervisor compose a vdpa device without any tool?
How can it tell ethtool, what is supported and what are the defaults?
I must be misunderstanding your comment about ethtool.
Can you please explain?
I am basically saying that we probably want to be able to change MAC
of a VDPA device on the host without desroying and recreating the
device as long as it's not in use.
Ok. I understood your comment now.
Yes, this was the objective which is why they are present as independent
config knob.
Jason was suggesting to have them as creation only knobs, which requires
recreate.
I don't have strong opinion for either method.
Passing them at creation time is simpler for user.
If user needs the ability to modify and reuse same device with different
config, extending such support in future like this patch should possible.
So there are two questions to close.
1. Can we start with config params at vdpa device creation time?
I'm not sure whether we need both but I'd like to see a full API and I think we
all agree host wants ability to tweak mac after device creation even if guest is
not allowed to change mac, right?
Yes.
$ vdpa dev add name foo mgmtdev pci/0000:03:00.0 mac 00:11:22:33:44:55 maxvqs 8 mtu 9000
Above API if we do at creation time. It is likely simpler for user to pass necessary params during creation time.
2. Is it ok to have these config params as individual fields at netlink U->K
UAPI level?
This is the method proposed in this patch series.
(Similar to incrementally growing vxlan ip link command).
Or
They should be packed in a structure between U-> K and deal with
typecasting based on size and more?
(Jason's input).
I'm inclined to say vxlan is closer to a model to follow.
Ok. thanks for the feedback. We are using the model close to vxlan.
Lets resolve should we have it at creation time, post creation or both?
(a) Creation time
Pros:
- simpler single api for user
- eliminates needs of inventing stats reset in future series
Cons:
- inability to reuse the device with different config
This can be solved by destroying the instance and re-creating it with
a different params?
- This may not be of great advantage, and it is probably fine to have creation time params
(b) post creation time:
Pros:
- able to reuse the device with different config for say different VM.
- will require stats reset in future once stats are implemented
Any reason for doing this other than re-creating the device?
Permissions.
I would expect that CAP_NET_ADMIN is required for both cases.
Or anything I miss here?
Thanks
Cons:
- more commands for users to config a device, better to have the ability at create time.
We probably need to support post creation but it should be device specific.
E.g we may support device resize for virtio-blk devices.
But it can be done on top I think.
Thanks
--
MST
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