Re: [PATCH linux-next v3 0/6] vdpa: enable user to set mac, mtu

From: Jason Wang <jasowang@redhat.com>
To: Parav Pandit <parav@nvidia.com>
Cc: Eli Cohen <elic@nvidia.com>,
	"virtualization@lists.linux-foundation.org"
	<virtualization@lists.linux-foundation.org>,
	"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH linux-next v3 0/6] vdpa: enable user to set mac, mtu
Date: Thu, 19 Aug 2021 12:18:44 +0800	[thread overview]
Message-ID: <9a88dea1-dc45-a196-f16d-ba3848ca0668@redhat.com> (raw)
In-Reply-To: <PH0PR12MB5481EF1FFD6EED706E831C89DCFF9@PH0PR12MB5481.namprd12.prod.outlook.com>

在 2021/8/18 下午12:36, Parav Pandit 写道:
>
>> From: Jason Wang <jasowang@redhat.com>
>> Sent: Wednesday, August 18, 2021 10:02 AM
>> On Wed, Aug 18, 2021 at 11:15 AM Parav Pandit <parav@nvidia.com> wrote:
> [..]
>>>> 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?
>>
> Yes, which is what I tried be say below.
>
>>> - This may not be of great advantage, and it is probably fine to have creation time params
>        ^^^^^ here.

Oh right, I miss this since it belongs to the bullets of "cons".

>
>>> (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?
>>
> No. Only reason I can think of is, device reconfig may be faster than recreate.
> But I weigh user simplicity more at the beginning and optimizations to bring later if required.
>

Right, but it looks to me we should only allow the post-creation changes 
only if it is allowed by the spec.

E.g if we allow mac to be modified by the guest, it is not expected to 
be changed from the host.

>>> 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.
> True. Your below device resize is good example of it.
>
>> E.g we may support device resize for virtio-blk devices.
>>
>> But it can be done on top I think.
> I think so too.

Thanks

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