On Wed, Feb 09, 2022 at 10:27:25AM +0800, Jason Wang wrote: > > 在 2022/1/30 下午11:30, Michael S. Tsirkin 写道: > > On Sun, Jan 30, 2022 at 05:12:46PM +0200, Max Gurtovoy wrote: > > > On 1/30/2022 4:41 PM, Michael S. Tsirkin wrote: > > > > On Sun, Jan 30, 2022 at 11:56:30AM +0200, Max Gurtovoy wrote: > > > > > On 1/30/2022 11:40 AM, Michael S. Tsirkin wrote: > > > > > > On Sun, Jan 30, 2022 at 11:13:38AM +0200, Max Gurtovoy wrote: > > > > > > > On 1/29/2022 5:53 AM, Jason Wang wrote: > > > > > > > > On Fri, Jan 28, 2022 at 11:52 PM Michael S. Tsirkin > > > > > > > > <m...@redhat.com> wrote: > > > > > > > > > On Fri, Jan 28, 2022 at 04:49:34PM +0100, Cornelia Huck wrote: > > > > > > > > > > On Fri, Jan 28 2022, "Michael S. Tsirkin" <m...@redhat.com> > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > On Fri, Jan 28, 2022 at 01:14:14PM +0100, Cornelia Huck > > > > > > > > > > > wrote: > > > > > > > > > > > > On Mon, Jan 24 2022, Max Gurtovoy > > > > > > > > > > > > <mgurto...@nvidia.com> wrote: > > > > > > > > > > > > > +\section{Admin Virtqueues}\label{sec:Basic > > > > > > > > > > > > > Facilities of a Virtio Device / Admin Virtqueues} > > > > > > > > > > > > > + > > > > > > > > > > > > > +Admin virtqueue is used to send administrative > > > > > > > > > > > > > commands to manipulate > > > > > > > > > > > > > +various features of the device and/or to manipulate > > > > > > > > > > > > > various features, > > > > > > > > > > > > > +if possible, of another device within the same group > > > > > > > > > > > > > (e.g. PCI VFs of > > > > > > > > > > > > > +a parent PCI PF device are grouped together. These > > > > > > > > > > > > > devices can be > > > > > > > > > > > > > +optionally managed by its parent PCI PF using its > > > > > > > > > > > > > admin virtqueue.). > > > > > > > > > > > > > + > > > > > > > > > > > > > +Use of Admin virtqueue is negotiated by the > > > > > > > > > > > > > VIRTIO_F_ADMIN_VQ > > > > > > > > > > > > > +feature bit. > > > > > > > > > > > > > + > > > > > > > > > > > > > +Admin virtqueue index may vary among different > > > > > > > > > > > > > device types. > > > > > > > > > > > > So, my understanding is: > > > > > > > > > > > > - any device type may or may not support the admin vq > > > > > > > > > > > > - if the device type wants to be able to accommodate > > > > > > > > > > > > the admin vq, it > > > > > > > > > > > > also needs to specify where it shows up when the > > > > > > > > > > > > feature is negotiated > > > > > > > > > > > > > > > > > > > > > > > > Do we expect that eventually all device types will need > > > > > > > > > > > > to support the > > > > > > > > > > > > admin vq (if some use case comes along that will > > > > > > > > > > > > require all devices to > > > > > > > > > > > > participate, for example?) > > > > > > > > > > > I suspect yes. And that's one of the reasons why I'd > > > > > > > > > > > rather we had a > > > > > > > > > > > device independent way to locate the admin queue. There > > > > > > > > > > > are less > > > > > > > > > > > transports than device types. > > > > > > > > > > So, do we want to bite the bullet now and simply say that > > > > > > > > > > every device > > > > > > > > > > type has the admin vq as the last vq if the feature is > > > > > > > > > > negotiated? > > > > > > > > > > Should be straightforward for the device types that have a > > > > > > > > > > fixed number > > > > > > > > > > of vqs, and doable for those that have a variable amount > > > > > > > > > > (two device > > > > > > > > > > types are covered by this series anyway.) I think we need > > > > > > > > > > to put it with > > > > > > > > > > the device types, as otherwise the numbering of virtqueues > > > > > > > > > > could change > > > > > > > > > > in unpredictable ways with the admin vq off/on. > > > > > > > > > Well that only works once. The next thing we'll need we won't > > > > > > > > > be able to > > > > > > > > > make the last one ;) So I am inclined to add a per-transport > > > > > > > > > field that > > > > > > > > > gives the admin queue number. > > > > > > > > Technically, there's no need to use the same namespace for admin > > > > > > > > virtqueue if it has a dedicated notification area. If we go > > > > > > > > this way, > > > > > > > > we can simply use 0 as queue index for admin virtqueue. > > > > > > > Or we can use index 0xFFFF for admin virtqueue for compatibility. > > > > > > I think I'd prefer a register with the #. For example we might want > > > > > > to limit the # of VQs in order to pass extra data with the kick > > > > > > write. > > > > > So you are suggesting adding a new cfg_type (#define > > > > > VIRTIO_PCI_CAP_ADMIN_CFG 10) ? > > > > > > > > > > that will look something like: > > > > > > > > > > struct virtio_pci_admin_cfg { > > > > > > > > > > le32 queue_index; /* read only for the driver */ > > > > > > > > > > le16 queue_size; /* read-write */ > > > > > le16 queue_msix_vector; /* read-write */ > > > > > le16 queue_enable; /* read-write */ > > > > > le16 queue_notify_off; /* read-only for driver */ > > > > > le64 queue_desc; /* read-write */ > > > > > le64 queue_driver; /* read-write */ > > > > > le64 queue_device; /* read-write */ > > > > > le16 queue_notify_data; /* read-only for driver */ > > > > > le16 queue_reset; /* read-write */ > > > > > > > > > > }; > > > > > > > > > > instead of re-using the struct virtio_pci_common_cfg ? > > > > > > > > > > > > > > > or do you prefer extending the struct virtio_pci_common_cfg with "le16 > > > > > admin_queue_index; /* read only for the driver */ ? > > > > The later. Other transports will need this too. > > > > > > > > > > > > Cornelia has another idea which is that instead of > > > > adding just the admin queue register to all transports, > > > > we instead add a misc_config structure to all > > > > transports. Working basically like device specific config, > > > > but being device independent. For now it will only have > > > > a single le16 admin_queue_index register. > > > > > > > > For PCI we would thus add it with VIRTIO_PCI_CAP_MISC_CFG > > > > > > > > The point here is that we are making it easier to add > > > > more fields just like admin queue index in the future. > > > OK. > > > > > > #define VIRTIO_PCI_CAP_MISC_CFG 10 > > > > > > and > > > > > > struct virtio_pci_misc_cfg { > > > le16 admin_queue_index; /* read-only for driver */ > > > }; > > > > > > Is agreed by all for V3 ? instead of the net and blk AQ index definitions. > > We need to add it to MMIO and CCW I guess too. > > > I wonder how much useful is this. > > E.g for PCI we have an equation to calculate the queue notify address, if > device choose to use dedicated notify for each queue it will probably end up > with the last queue. > > And I think the admin_queue_index should be stable regardless of the feature > that has been negotiated? > > Thanks
there's only one last queue though. I wouldn't just use it and hope we don't need it for anything else. > > > > > This is Cornelia's idea, we'll need her response. > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > Another advantage to this approach is that > > > > > > > > > we can make sure admin queue gets a page by itself (which can > > > > > > > > > be good if > > > > > > > > > we want to allow access to regular vqs but not to the admin > > > > > > > > > queue to > > > > > > > > > guest) even if regular vqs share a page. Will help devices > > > > > > > > > use less > > > > > > > > > memory space. > > > > > > > > > > > > > > > > > > -- > > > > > > > > > MST > > > > > > > > > --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org