Re: [virtio-comment] Re: [PATCH v10 04/10] admin: introduce virtio admin virtqueues

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 07/03/2023 0:49, Michael S. Tsirkin wrote:
> On Mon, Mar 06, 2023 at 05:14:09PM +0200, Max Gurtovoy wrote:
> > > > This would allow pipelining
> > > > dependent commands but prevent long-running commands because the
> > > > virtqueue is blocked while executing a command.
> > >
> > > we have multiple vqs for that.
> >
> > why do we need multiple admin vqs ?
>
> You are literally replying to a discussion with a use-case.

I don't follow.

You are snipping my reply that explaining how to simplify the spec.
I don't think that any device will need more than single admin queue.

NVMe specification has a single admin queue, so why do we need to invent 
the wheel ?
And it has so many admin commands that may take time such as FW upgrade, 
format a block device, also we have vendor specific LM specification and 
we never thought in a direction of having multiple admin queues.
MQ was invented for increasing performance and not for preventing long 
running commands. Most of these commands are queued one by one in a sync 
manner.
For example:
- quiesce a device
- freeze a device
- save state
- load state
- configure msix
- configure feature bits

Virtio has a single cvq as well.

I'm asking if you can re-think please.
We have a non-spec prototypes for LM so please use our experience in 
this area.