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Re: device compatibility interface for live migration with assigned devices



On Wed, 19 Aug 2020 11:30:35 +0800
Yan Zhao <yan y zhao intel com> wrote:

> On Tue, Aug 18, 2020 at 09:39:24AM +0000, Parav Pandit wrote:
> > Hi Cornelia,
> >   
> > > From: Cornelia Huck <cohuck redhat com>
> > > Sent: Tuesday, August 18, 2020 3:07 PM
> > > To: Daniel P. Berrangé <berrange redhat com>
> > > Cc: Jason Wang <jasowang redhat com>; Yan Zhao
> > > <yan y zhao intel com>; kvm vger kernel org; libvir-list redhat com;
> > > qemu-devel nongnu org; Kirti Wankhede <kwankhede nvidia com>;
> > > eauger redhat com; xin-ran wang intel com; corbet lwn net; openstack-
> > > discuss lists openstack org; shaohe feng intel com; kevin tian intel com;
> > > Parav Pandit <parav mellanox com>; jian-feng ding intel com;
> > > dgilbert redhat com; zhenyuw linux intel com; hejie xu intel com;
> > > bao yumeng zte com cn; Alex Williamson <alex williamson redhat com>;
> > > eskultet redhat com; smooney redhat com; intel-gvt-
> > > dev lists freedesktop org; Jiri Pirko <jiri mellanox com>;
> > > dinechin redhat com; devel ovirt org
> > > Subject: Re: device compatibility interface for live migration with assigned
> > > devices
> > > 
> > > On Tue, 18 Aug 2020 10:16:28 +0100
> > > Daniel P. Berrangé <berrange redhat com> wrote:
> > >   
> > > > On Tue, Aug 18, 2020 at 05:01:51PM +0800, Jason Wang wrote:  
> > > > >    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:  
> > > >  
> > > > >  we actually can also retrieve the same information through sysfs,
> > > > > .e.g
> > > > >
> > > > >  |- [path to device]
> > > > >     |--- migration
> > > > >     |     |--- self
> > > > >     |     |   |---device_api
> > > > >     |    |   |---mdev_type
> > > > >     |    |   |---software_version
> > > > >     |    |   |---device_id
> > > > >     |    |   |---aggregator
> > > > >     |     |--- compatible
> > > > >     |     |   |---device_api
> > > > >     |    |   |---mdev_type
> > > > >     |    |   |---software_version
> > > > >     |    |   |---device_id
> > > > >     |    |   |---aggregator
> > > > >
> > > > >
> > > > >  Yes but:
> > > > >
> > > > >  - You need one file per attribute (one syscall for one attribute)
> > > > >  - Attribute is coupled with kobject  
> > > 
> > > Is that really that bad? You have the device with an embedded kobject
> > > anyway, and you can just put things into an attribute group?
> > > 
> > > [Also, I think that self/compatible split in the example makes things
> > > needlessly complex. Shouldn't semantic versioning and matching already
> > > cover nearly everything? I would expect very few cases that are more
> > > complex than that. Maybe the aggregation stuff, but I don't think we need
> > > that self/compatible split for that, either.]
> > >   
> > > > >
> > > > >  All of above seems unnecessary.
> > > > >
> > > > >  Another point, as we discussed in another thread, it's really hard
> > > > > to make  sure the above API work for all types of devices and
> > > > > frameworks. So having a  vendor specific API looks much better.
> > > > >
> > > > >  From the POV of userspace mgmt apps doing device compat checking /
> > > > > migration,  we certainly do NOT want to use different vendor
> > > > > specific APIs. We want to  have an API that can be used / controlled in a  
> > > standard manner across vendors.  
> > > > >
> > > > >    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 ...  
> > > >
> > > > NB, I was not questioning devlink vs sysfs directly. If devlink is
> > > > related to netlink, I can't say I'm enthusiastic as IMKE sysfs is
> > > > easier to deal with. I don't know enough about devlink to have much of an  
> > > opinion though.  
> > > > The key point was that I don't want the userspace APIs we need to deal
> > > > with to be vendor specific.  
> > > 
> > > From what I've seen of devlink, it seems quite nice; but I understand why
> > > sysfs might be easier to deal with (especially as there's likely already a lot of
> > > code using it.)
> > > 
> > > I understand that some users would like devlink because it is already widely
> > > used for network drivers (and some others), but I don't think the majority of
> > > devices used with vfio are network (although certainly a lot of them are.)
> > >   
> > > >
> > > > What I care about is that we have a *standard* userspace API for
> > > > performing device compatibility checking / state migration, for use by
> > > > QEMU/libvirt/ OpenStack, such that we can write code without countless
> > > > vendor specific code paths.
> > > >
> > > > If there is vendor specific stuff on the side, that's fine as we can
> > > > ignore that, but the core functionality for device compat / migration
> > > > needs to be standardized.  
> > > 
> > > To summarize:
> > > - choose one of sysfs or devlink
> > > - have a common interface, with a standardized way to add
> > >   vendor-specific attributes
> > > ?  
> > 
> > Please refer to my previous email which has more example and details.  
> hi Parav,
> the example is based on a new vdpa tool running over netlink, not based
> on devlink, right?
> For vfio migration compatibility, we have to deal with both mdev and physical
> pci devices, I don't think it's a good idea to write a new tool for it, given
> we are able to retrieve the same info from sysfs and there's already an
> mdevctl from Alex (https://github.com/mdevctl/mdevctl).
> 
> hi All,
> could we decide that sysfs is the interface that every VFIO vendor driver
> needs to provide in order to support vfio live migration, otherwise the
> userspace management tool would not list the device into the compatible
> list?
> 
> if that's true, let's move to the standardizing of the sysfs interface.
> (1) content
> common part: (must)
>    - software_version: (in major.minor.bugfix scheme)
>    - device_api: vfio-pci or vfio-ccw ...
>    - type: mdev type for mdev device or
>            a signature for physical device which is a counterpart for
> 	   mdev type.
> 
> device api specific part: (must)
>   - pci id: pci id of mdev parent device or pci id of physical pci
>     device (device_api is vfio-pci)

As noted previously, the parent PCI ID should not matter for an mdev
device, if a vendor has a dependency on matching the parent device PCI
ID, that's a vendor specific restriction.  An mdev device can also
expose a vfio-pci device API without the parent device being PCI.  For
a physical PCI device, shouldn't the PCI ID be encompassed in the
signature?  Thanks,

Alex

>   - subchannel_type (device_api is vfio-ccw) 
>  
> vendor driver specific part: (optional)
>   - aggregator
>   - chpid_type
>   - remote_url
> 
> NOTE: vendors are free to add attributes in this part with a
> restriction that this attribute is able to be configured with the same
> name in sysfs too. e.g.
> for aggregator, there must be a sysfs attribute in device node
> /sys/devices/pci0000:00/0000:00:02.0/882cc4da-dede-11e7-9180-078a62063ab1/intel_vgpu/aggregator,
> so that the userspace tool is able to configure the target device
> according to source device's aggregator attribute.
> 
> 
> (2) where and structure
> proposal 1:
> |- [path to device]
>   |--- migration
>   |     |--- self
>   |     |    |-software_version
>   |     |    |-device_api
>   |     |    |-type
>   |     |    |-[pci_id or subchannel_type]
>   |     |    |-<aggregator or chpid_type>
>   |     |--- compatible
>   |     |    |-software_version
>   |     |    |-device_api
>   |     |    |-type
>   |     |    |-[pci_id or subchannel_type]
>   |     |    |-<aggregator or chpid_type>
> multiple compatible is allowed.
> attributes should be ASCII text files, preferably with only one value
> per file.
> 
> 
> proposal 2: use bin_attribute.
> |- [path to device]
>   |--- migration
>   |     |--- self
>   |     |--- compatible
> 
> so we can continue use multiline format. e.g.
> cat compatible
>   software_version=0.1.0
>   device_api=vfio_pci
>   type=i915-GVTg_V5_{val1:int:1,2,4,8}
>   pci_id=80865963
>   aggregator={val1}/2
> 
> Thanks
> Yan
> 



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