Re: [virtio-comment] About the plan of Admin Queue

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Mon, 3 Jul 2023 16:01:35 +0800, "Zhu, Lingshan" <lingshan.zhu@intel.com> wrote:
>
>
> On 7/3/2023 1:54 PM, Xuan Zhuo wrote:
> > On Mon, 3 Jul 2023 12:29:32 +0800, "Zhu, Lingshan" <lingshan.zhu@intel.com> wrote:
> >>
> >> On 6/30/2023 7:35 PM, Parav Pandit wrote:
> >>>> From: virtio-comment@lists.oasis-open.org <virtio-comment@lists.oasis-
> >>>> open.org> On Behalf Of Zhu, Lingshan
> >>>> Sent: Friday, June 30, 2023 6:33 AM
> >>>>
> >>>>>>> Can we let the DPU notify the driver to create a new devicer from the
> >>>> backend?
> >>> Yes, why not.
> >>>
> >>>>>>> The key point is who want to create a new device.
> >>>>>> DPU can come with a certain number of pre-created ADIs, just make
> >>>>>> sure the orchestration SW is aware of their device IDs.
> >>>>>>
> >>> Cloud often need these devices to be created dynamically, many a time after the host OS is booted.
> >>> To be more generic, those devices to be created and connected to the host regardless of the life cycle of the host.
> >>> Xuan partly explained it.
> >>>
> >>>>>> If you want the DPU randomly create ADIs and notify the driver, I
> >>>>>> think we need interrupt, e.g., re-use config interrupt. But why DPU
> >>>>>> wants to create and hot plug in a device to a guest?
> >>>>>> Shall the host handle that or DPU pre-create then expose to baremteal
> >>>>>> machines?
> >>>>> In your scenario, the supervisor is on the os, which controls the DPU
> >>>>> to create new devices.
> >>>>>
> >>>>> In the cloud scenario, the vendor manager is in the DPU, and the
> >>>>> entire host is for users. Of course, there are situations where the
> >>>>> vendor manager are in the HOST. But for bare metal machines, the host
> >>>>> belongs to the customer, the vendor manager is only in the DPU.
> >>>>>
> >>>>> So when the customers buy a new nic for the host, the vendor manager
> >>>>> will plug a device to the host from the DPU.
> >>>> I understand once a customer orders a new NIC, you wants to present the NIC
> >>>> to the host.
> >>>> However you only owns the DPU and the customer owns the host, that means
> >>>> this creation and hot plug must be transparent to the host and there may not be
> >>>> a host driver help handling an interrupt/probe.
> >>>>
> >>> That is ok. when driver is loaded, it would query about its child devices and probe it, if we strictly want to follow SIOV model.
> >>>
> >>>> However this is not PCI which has a tree/switch and can enumerate devices to
> >>>> the host by spanning the device across the PCI hierarchy.
> >>>>
> >>> Those enumeration is triggered by the parent PCI device and pci bridge and switch will also discover it.
> >>>
> >>>> To address an ADI, there is only a device_id.
> >>>>
> >>> SIOV device must have a unique identifier at PCI bus level for sure.
> >>> I cannot speak more about it in this forum due to other logistics issue.
> >>> But assume that there is PCI level unique identifier for SIOV device that switches on the path will learn about.
> >>>
> >>>> So, do you mind share how your DPU offload the device model? What kind of
> >>>> device your DPU provide to the host? Lets see whether DPU can mediate this by
> >>>> its own?
> >>>>
> >>> It is a virtio nic, blk and other virtio devices for us.
> >>> A DPU hotplugs a device, host side either gets interrupt or later gets to know about it when explicitly queries.
> >>> There is no mediation per say here, it is just a dpu based SIOV device like a regular PF.
> >>>
> >>> For non virtio DPU device, I implemented them in Linux for dpus 2 years ago.
> >>> You might find a Linux reference model useful at [1].
> >>> A usage model already exists in one OS and in use for non virtio devices.
> >>> This certainly works without SIOV unique PCI device identifiers, because DPU (non-host) managed SIOV device spec still does not exist.
> >>>
> >>> For virtio, I think we should wait for this piece to be defined and leverage that, instead of virtio tc creating its own.
> >>>
> >>> [1] https://github.com/Mellanox/scalablefunctions/wiki
> >> well I see SF facing the similar challenge, I can add a command for the
> >> driver to query all existing SIOV ADIs of a device,
> >> and the device return ADIs id and status. Looks good? and work for you
> >> @Xuan?
> > Can the device notifies the driver by a interrupt?
> Of course this can be an option as previously discussed.
> That would be a config interrupt(with proper suppression) from the
> management device,
> which requires a new cap in a bar, then you still need to fetch the
> information.
>
> A proposal:
>
> a new cap, at least contains:
> total number of the ADIs.
>
> Then once any ADIs are created or removed, the PF driver get a notification.
>
> Works for you?


Look good to me.

Thanks.


> >
> > Thanks.
> >
> >
> >> Thanks
> >>
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