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

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Mar 09, 2023 at 01:04:30PM +0000, Parav Pandit wrote:
> 
> > From: Jiri Pirko <jiri@nvidia.com>
> > Sent: Thursday, March 9, 2023 2:31 AM
> > 
> > Wed, Mar 08, 2023 at 10:25:32PM CET, parav@nvidia.com wrote:
> > >
> > >> From: virtio-comment@lists.oasis-open.org
> > >> <virtio-comment@lists.oasis- open.org> On Behalf Of David Edmondson
> > >
> > >> In support of live migration, might we end up moving large amounts of
> > >> device state through the admin queue?
> > >>
> > >Correct.
> > >
> > >> If so, that would seem to have some performance requirements, though
> > >> I don't know if it would justify multiple admin queues.
> > >DMA of the data through the proposed AQ is supported.
> > >
> > >If I understood Max correctly when Max said " This AQ is not aimed for
> > >performance ", he means that AQ doesn't have performance requirements as
> > io/network queues to complete millions of ops/sec.
> > >
> > >it is several hundred to maybe (on the higher side) thousand ops/sec during
> > LM, provisioning use case.
> > 
> > But isn't it good to design it for performance from start? I mean, state transfer
> > of thousands of VFs at a time is definitelly performance related, isn't it?
> > 
> It is. Which part of the proposed AQ doesn't cover this aspect?
> The only issue that I see today is, that a given GET family of commands q contains the read-only and write-only descriptors which require multiple dma allocations on driver side.

BTW for a while now I wanted to add a descriptor flag that
will stick data inline in the descriptor. Perfect for passing
small bits of data such as vqn, or the virtio header.


> > 
> > >
> > >DMA perspective as you mentioned, AQ still has the same perf requirements
> > as that of regular nw/blk io queues.