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Subject: Re: [PATCH 4/5] virtio-net: add support for VIRTIO_F_ADMIN_VQ


On Mon, Jan 17, 2022 at 02:07:51PM +0000, Parav Pandit wrote:
> 
> > From: Max Gurtovoy <mgurtovoy@nvidia.com>
> > Sent: Sunday, January 16, 2022 3:18 PM
> > 
> > 
> > On 1/13/2022 7:56 PM, Michael S. Tsirkin wrote:
> > > On Thu, Jan 13, 2022 at 04:51:02PM +0200, Max Gurtovoy wrote:
> > >> Set the relevant index in case of VIRTIO_F_ADMIN_VQ negotiation.
> > >>
> > >> Reviewed-by: Parav Pandit <parav@nvidia.com>
> > >> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > So admin VQ # is only known when all features are negotiated.
> > 
> > No. The driver should see if VIRTIO_NET_F_CTRL_VQ/VIRTIO_F_ADMIN_VQ
> > are set by the device.
> > 
> > Negotiation is not a must.
> > 
> > Lets say CTRL_VQ is supported by the device and driver A would like to use it
> > and driver B wouldn't like to use it - in both cases the admiq VQ # would be 2N
> > + 1.
> > 
> > > Which is quite annoying if hypervisor wants to partition things e.g.
> > > handling admin q in process and handling vqs by an external process or
> > > by hardware.
> > >
> > > I think we can allow devices to set the VQ# for the admin queue
> > > instead. Would that work?
> Number of MSI-X configuration and number of VQs config are two different,


I was talking about the number of the VQ used for admin commands. Not
about the number of VQs.

> though it has strong correlation.
> Configuring number of queues seems a very device specific configuration (even though num_queues is generic field in struct virtio_pci_common_cfg).
> 
> So num VQ configuration is a different command likely combined with other device specific config such as mac or rss or others.

I was not talking about that at all, but since you mention that,
to me it looks like something that many device types can support.
It's not necessarily rss related, MQ config would benefit too,
so I am not sure why not have a command for controlling number
of queues. Looks like it could quite be generic.

Since current guests only support two modes: a vector
per VQ and a shared vector for all VQs, it follows that
it is important when configuring vectors per VF to also configure
VQs per VF. This makes me wonder whether ability to configure
vectors per VF in isolation without ability to configure or
at least query VQs per VF even has value.


-- 
MST



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