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Well,I see. Thanks to Sean for your detailed answer!
On 12/14/2021 00:33，Sean Mooney<smooney at redhat.com> wrote：
On Mon, 2021-12-13 at 09:54 +0800, Di XiaoLi wrote:
hi, Cyborg and nova team:
I am using cyborg with "Wallaby" release to manage my accelerator devices, while I'm trying to unbind the accelerator I found that the device was not actually unbound from the virtual machine.
Here are my questions:
1. What is the function of the arq unbind command in cyborg ?
it has two usecases.
it call by nova when nova is deleting or moving the vm
it can be used by an enduser if they are not using cybrog with nova.
2. How to unbind the accelerator which bounded to vm? Does nova or cyborg support this function now？

the only way to  do that for a nova instance is to resize it to a flavor that does not request the device via the
cyborg device profiel in the extra spec.

more recently we have started to support using cybrog for neutron nics too.
in this case the unbinding can be done by doing a port detach and the device should be remvoed from the vm and unbond in cybrog.

Here are my steps:
step1: openstack accelerator arq unbind ed205084-f58d-4fad-99b4-327a1398858f
this should be treated as an admin/service only oepration wehn using cybrog with nova more on that below.
+---------------------+--------------------------------------+
Field               | Value                                |
+---------------------+--------------------------------------+
uuid                | ed205084-f58d-4fad-99b4-327a1398858f |
state               | Unbound                              |
device_profile_name | ssd                                  |
hostname            | None                                 |
device_rp_uuid      | None                                 |
instance_uuid       | None                                 |
attach_handle_type  |                                      |
attach_handle_info  | {}                                   |
+---------------------+--------------------------------------+

step2: login vm and check the device, but it still here.
step3: stop vm and start vm, met the following error:
"nova.exception.AcceleratorRequestOpFailed: Failed to get accelerator requests: Cyborg returned no accelerator requests for instance ca77ef4e-421c-4c6c-9d76-7618a90ec921"
that is what i would expect and is the correct behavior as you violated the contract between nova and cyborg by unbindng the arq.

when useing cyborg with nova you shoudl never use the cyborg api driectly expcit to list the devcice profiles.
you should treat it like placment in that regard.
cybrog when used with nova today is an internal service that end user should at most have read only access too list the profiles.

nova does not support cybrog device hot/cold attach or detach.
the only way to add or remove a device form cyborg via nova is the device profile request in the flavor.
so the only support opartion to change the attach device is resize to a differnt flavor.

as i said above if you are attching smartnics using cyborg via neutron then you can also attach/devatch cybrog device by attaching/detaching
the neutron port which contains the device profile request. note that if the deivce does not exist on the currnt host the attch will likely fail.
detach should more or less always work unless there is an internal errror with one of the 3 service invovled.



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