RE: device compatibility interface for live migration with assigned devices

[Parav Pandit <parav@nvidia.com>]

> From: Jason Wang <jasowang@redhat.com>
> Sent: Wednesday, August 19, 2020 12:19 PM
> 
> 
> On 2020/8/19 下午1:26, Parav Pandit wrote:
> >
> >> From: Jason Wang <jasowang@redhat.com>
> >> Sent: Wednesday, August 19, 2020 8:16 AM
> >
> >> On 2020/8/18 下午5:32, Parav Pandit wrote:
> >>> Hi Jason,
> >>>
> >>> From: Jason Wang <jasowang@redhat.com>
> >>> Sent: Tuesday, August 18, 2020 2:32 PM
> >>>
> >>>
> >>> On 2020/8/18 下午4:55, Daniel P. Berrangé wrote:
> >>> On Tue, Aug 18, 2020 at 11:24:30AM +0800, Jason Wang wrote:
> >>> On 2020/8/14 下午1:16, Yan Zhao wrote:
> >>> On Thu, Aug 13, 2020 at 12:24:50PM +0800, Jason Wang wrote:
> >>> On 2020/8/10 下午3:46, Yan Zhao wrote:
> >>> driver is it handled by?
> >>> It looks that the devlink is for network device specific, and in
> >>> devlink.h, it says include/uapi/linux/devlink.h - Network physical
> >>> device Netlink interface, Actually not, I think there used to have
> >>> some discussion last year and the conclusion is to remove this
> >>> comment.
> >>>
> >>> [...]
> >>>
> >>>> Yes, but it could be hard. E.g vDPA will chose to use devlink
> >>>> (there's a long
> >> debate on sysfs vs devlink). So if we go with sysfs, at least two
> >> APIs needs to be supported ...
> >>> We had internal discussion and proposal on this topic.
> >>> I wanted Eli Cohen to be back from vacation on Wed 8/19, but since
> >>> this is
> >> active discussion right now, I will share the thoughts anyway.
> >>> Here are the initial round of thoughts and proposal.
> >>>
> >>> User requirements:
> >>> ---------------------------
> >>> 1. User might want to create one or more vdpa devices per PCI PF/VF/SF.
> >>> 2. User might want to create one or more vdpa devices of type
> >>> net/blk or
> >> other type.
> >>> 3. User needs to look and dump at the health of the queues for debug
> purpose.
> >>> 4. During vdpa net device creation time, user may have to provide a
> >>> MAC
> >> address and/or VLAN.
> >>> 5. User should be able to set/query some of the attributes for
> >>> debug/compatibility check 6. When user wants to create vdpa device,
> >>> it needs
> >> to know which device supports creation.
> >>> 7. User should be able to see the queue statistics of doorbells,
> >>> wqes etc regardless of class type
> >>
> >> Note that wqes is probably not something common in all of the vendors.
> > Yes. I virtq descriptors stats is better to monitor the virtqueues.
> >
> >>
> >>> To address above requirements, there is a need of vendor agnostic
> >>> tool, so
> >> that user can create/config/delete vdpa device(s) regardless of the vendor.
> >>> Hence,
> >>> We should have a tool that lets user do it.
> >>>
> >>> Examples:
> >>> -------------
> >>> (a) List parent devices which supports creating vdpa devices.
> >>> It also shows which class types supported by this parent device.
> >>> In below command two parent devices support vdpa device creation.
> >>> First is PCI VF whose bdf is 03.00:5.
> >>> Second is PCI SF whose name is mlx5_sf.1
> >>>
> >>> $ vdpa list pd
> >>
> >> What did "pd" mean?
> >>
> > Parent device which support creation of one or more vdpa devices.
> > In a system there can be multiple parent devices which may be support vdpa
> creation.
> > User should be able to know which devices support it, and when user creates a
> vdpa device, it tells which parent device to use for creation as done in below
> vdpa dev add example.
> >>> pci/0000:03.00:5
> >>>     class_supports
> >>>       net vdpa
> >>> virtbus/mlx5_sf.1
> >>
> >> So creating mlx5_sf.1 is the charge of devlink?
> >>
> > Yes.
> > But here vdpa tool is working at the parent device identifier {bus+name}
> instead of devlink identifier.
> >
> >
> >>>     class_supports
> >>>       net
> >>>
> >>> (b) Now add a vdpa device and show the device.
> >>> $ vdpa dev add pci/0000:03.00:5 type net
> >>
> >> So if you want to create devices types other than vdpa on
> >> pci/0000:03.00:5 it needs some synchronization with devlink?
> > Please refer to FAQ-1,  a new tool is not linked to devlink because vdpa will
> evolve with time and devlink will fall short.
> > So no, it doesn't need any synchronization with devlink.
> > As long as parent device exist, user can create it.
> > All synchronization will be within drivers/vdpa/vdpa.c This user
> > interface is exposed via new netlink family by doing genl_register_family() with
> new name "vdpa" in drivers/vdpa/vdpa.c.
> 
> 
> Just to make sure I understand here.
> 
> Consider we had virtbus/mlx5_sf.1. Process A want to create a vDPA instance on
> top of it but Process B want to create a IB instance. Then I think some
> synchronization is needed at at least parent device level?

Likely but rdma device will be created either through 
$ rdma link add command.
Or auto created by driver because there is only one without much configuration.

While vdpa device(s) for virtbus/mlx5_sf.1 will be created through vdpa subsystem.
And vdpa's synchronization will be contained within drivers/vdpa/vdpa.c

> 
> 
> >
> >>
> >>> $ vdpa dev show
> >>> vdpa0@pci/0000:03.00:5 type net state inactive maxqueues 8 curqueues
> >>> 4
> >>>
> >>> (c) vdpa dev show features vdpa0
> >>> iommu platform
> >>> version 1
> >>>
> >>> (d) dump vdpa statistics
> >>> $ vdpa dev stats show vdpa0
> >>> kickdoorbells 10
> >>> wqes 100
> >>>
> >>> (e) Now delete a vdpa device previously created.
> >>> $ vdpa dev del vdpa0
> >>>
> >>> Design overview:
> >>> -----------------------
> >>> 1. Above example tool runs over netlink socket interface.
> >>> 2. This enables users to return meaningful error strings in addition
> >>> to code so
> >> that user can be more informed.
> >>> Often this is missing in ioctl()/configfs/sysfs interfaces.
> >>> 3. This tool over netlink enables syscaller tests to be more usable
> >>> like other
> >> subsystems to keep kernel robust
> >>> 4. This provides vendor agnostic view of all vdpa capable parent and
> >>> vdpa
> >> devices.
> >>> 5. Each driver which supports vdpa device creation, registers the
> >>> parent device
> >> along with supported classes.
> >>> FAQs:
> >>> --------
> >>> 1. Why not using devlink?
> >>> Ans: Because as vdpa echo system grows, devlink will fall short of
> >>> extending
> >> vdpa specific params, attributes, stats.
> >>
> >>
> >> This should be fine but it's still not clear to me the difference
> >> between a vdpa netlink and a vdpa object in devlink.
> >>
> > The difference is a vdpa specific tool work at the parent device level.
> > It is likely more appropriate to because it can self-contain everything needed
> to create/delete devices, view/set features, stats.
> > Trying to put that in devlink will fall short as devlink doesn’t have vdpa
> definitions.
> > Typically when a class/device subsystem grows, its own tool is wiser like
> iproute2/ip, iproute2/tc, iproute2/rdma.
> 
> 
> Ok, I see.
> 
> Thanks
>