virtio — archive

[Michael S. Tsirkin]

On Wed, Apr 27, 2022 at 01:58:17AM +0300, Max Gurtovoy wrote: > Hi, > A device group definition will help extending the virtio specefication for > various future features that require a notion of grouping devices together or > managing devices inside a group. A device group include one or more virtio devices. > For now, only support for type 1 device group was added. OK good progress here. Sent a bunch of comments, most of them cosmetic. > Also introduce the admin facility to allow manipulating features and configurations > in a generic manner. Using the admin command set, one can manipulate the device itself > and/or to manipulate, if possible, another device within the same device group (for now, > introduce only support of PCI SR-IOV devices grouping). > > The admin command set will be extended in the future to support more functionalities. > Some of these functionalities are already under discussions. > > The admin virtqueue is the first management interface to issue admin commands from > the admin command set. > > Motivation for choosing admin queue as first management interface: > 1. It is anticipated that admin queue will be used for managing and configuring > many different type of resources. For example, > a. PCI PF configuring PCI VF attributes. > b. virtio device creating/destroying/configuring subfunctions discussed in [1] > c. composing device config space of VF or SF such as mac address, number of VQs, virtio features > > Mapping all of them as configuration registers to MMIO will require large MMIO space, > if done for each VF/SF. Such MMIO implementation in physical devices such as PCI PF and VF > requires on-chip resources to complete within MMIO access latencies. Such resources are very > expensive. > > 2. Such limitation can be overcome by having smaller MMIO register set to build > a command request response interface. However, such MMIO based command interface > will be limited to serve single outstanding command execution. Such limitation can > resulting in high device creation and composing time which can affect VM startup time. > Often device can queue and service multiple commands in parallel, such command interface > cannot use parallelism offered by the device. > > 3. When a command wants to DMA data from one or more physical addresses, for example in the future a > live migration command may need to fetch device state consist of config space, tens of > VQs state, VLAN and MAC table, per VQ partial outstanding block IO list database and more. > Packing one or more DMA addresses over new command interface will be burden some and continue > to suffer single outstanding command execution latencies. Such limitation is not good for time > sensitive live migration use cases. > > 4. A virtio queue overcomes all the above limitations. It also supports DMA and multiple outstanding > descriptors. Similar mechanism exist today for device specific configuration - the control VQ. > > A future work can add another management interface to issue admin commands. > > [1] https://lists.oasis-open.org/archives/virtio-comment/202108/msg00025.html > > This series include the comments and fixes from V1-V4 of the initial patch sets ("VIRTIO: Provision maximum > MSI-X vectors for a VF" and "Introduce virtio subsystem and Admin virtqueue" [2]). > This series was extended with additional RFC for setting managed device feature bits as another example for > using admin command set. Also device/driver negotiation for admin caps was introduced as a response for previous > comments on the mailing list. > > [2] https://lists.oasis-open.org/archives/virtio-comment/202203/msg00005.html > > > Open issues: > 1. CCW and MMIO specification for admin_queue_index register > > Changelog: > - Merged MSI-X configuration series to current one. > - Addressed comments from MST, Jason Wang and others. > - simplified the interface. > - added another resource management as RFC (feature bits). > > Max Gurtovoy (7): > Introduce device group > Introduce admin command set > Introduce new destination type for admin commands > Introduce virtio admin virtqueue > Add miscellaneous configuration structure for PCI > Introduce MGMT admin commands > RFC: add initial support for configuring feature bits > > admin.tex | 282 +++++++++++++++++++++++++++++++++++++++++++++++ > conformance.tex | 3 + > content.tex | 118 +++++++++++++++++++- > introduction.tex | 42 +++++++ > 4 files changed, 443 insertions(+), 2 deletions(-) > create mode 100644 admin.tex > > -- > 2.21.0