[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: Re: [PATCH v1 0/5] Introduce virtio subsystem and Admin virtqueue
On Wed, Mar 02, 2022 at 05:56:03PM +0200, Max Gurtovoy wrote: > Hi, > A virtio subsystem 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. It also might be used splitting or sharing a > single virtio backend between multiple devices (e.g. Multipath IO for virtio-blk > devices). A virtio subsystem include one or more virtio devices. A large patch, need a bit more time for review. Meanwhile, how about adding migration related capabilities? I would very much like that to make progress before people start using high overhead solutions like VQ shadowing. > 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 virtio subsystem (the > following patch set). > > The admin virtqueue is the first management interface to issue Admin commands from > the admin command set. > > The admin virtqueue interface will be extended in the future with more and more > features that some of them already in discussions. Some of these features don't > fit to MMIO/config_space characteristics, therefore a queue is selected to address > admin commands. > > Motivation for choosing admin queue: > 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. > > [1] https://lists.oasis-open.org/archives/virtio-comment/202108/msg00025.html > > This series was extended and splitted from the V3 of the "VIRTIO: Provision maximum MSI-X vectors for a VF". > This series include the comments and fixes from V1-V3 of the initial patch set from above. > The following series introduce the management devices and MSI-X configuration of virtio devices. > > Open issues: > 1. CCW and MMIO specification for admin_queue_index register > > Max Gurtovoy (5): > virtio: Introduce virtio subsystem > Introduce Admin Command Set > Introduce DEVICE INFO Admin command > Add virtio Admin virtqueue > Add miscellaneous configuration structure for PCI > > admin.tex | 177 +++++++++++++++++++++++++++++++++++++++++++++++ > conformance.tex | 3 + > content.tex | 33 ++++++++- > introduction.tex | 20 ++++++ > 4 files changed, 231 insertions(+), 2 deletions(-) > create mode 100644 admin.tex > > -- > 2.21.0
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]