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Re: device compatibility interface for live migration with assigned devi
From: |
Dr. David Alan Gilbert |
Subject: |
Re: device compatibility interface for live migration with assigned devices |
Date: |
Wed, 15 Jul 2020 09:23:09 +0100 |
User-agent: |
Mutt/1.14.5 (2020-06-23) |
* Alex Williamson (alex.williamson@redhat.com) wrote:
> On Tue, 14 Jul 2020 18:19:46 +0100
> "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
>
> > * Alex Williamson (alex.williamson@redhat.com) wrote:
> > > On Tue, 14 Jul 2020 11:21:29 +0100
> > > Daniel P. Berrangé <berrange@redhat.com> wrote:
> > >
> > > > On Tue, Jul 14, 2020 at 07:29:57AM +0800, Yan Zhao wrote:
> > > > > hi folks,
> > > > > we are defining a device migration compatibility interface that helps
> > > > > upper
> > > > > layer stack like openstack/ovirt/libvirt to check if two devices are
> > > > > live migration compatible.
> > > > > The "devices" here could be MDEVs, physical devices, or hybrid of the
> > > > > two.
> > > > > e.g. we could use it to check whether
> > > > > - a src MDEV can migrate to a target MDEV,
> > > > > - a src VF in SRIOV can migrate to a target VF in SRIOV,
> > > > > - a src MDEV can migration to a target VF in SRIOV.
> > > > > (e.g. SIOV/SRIOV backward compatibility case)
> > > > >
> > > > > The upper layer stack could use this interface as the last step to
> > > > > check
> > > > > if one device is able to migrate to another device before triggering
> > > > > a real
> > > > > live migration procedure.
> > > > > we are not sure if this interface is of value or help to you. please
> > > > > don't
> > > > > hesitate to drop your valuable comments.
> > > > >
> > > > >
> > > > > (1) interface definition
> > > > > The interface is defined in below way:
> > > > >
> > > > > __ userspace
> > > > > /\ \
> > > > > / \write
> > > > > / read \
> > > > > ________/__________ ___\|/_____________
> > > > > | migration_version | | migration_version |-->check migration
> > > > > --------------------- --------------------- compatibility
> > > > > device A device B
> > > > >
> > > > >
> > > > > a device attribute named migration_version is defined under each
> > > > > device's
> > > > > sysfs node. e.g.
> > > > > (/sys/bus/pci/devices/0000\:00\:02.0/$mdev_UUID/migration_version).
> > > > > userspace tools read the migration_version as a string from the
> > > > > source device,
> > > > > and write it to the migration_version sysfs attribute in the target
> > > > > device.
> > > > >
> > > > > The userspace should treat ANY of below conditions as two devices not
> > > > > compatible:
> > > > > - any one of the two devices does not have a migration_version
> > > > > attribute
> > > > > - error when reading from migration_version attribute of one device
> > > > > - error when writing migration_version string of one device to
> > > > > migration_version attribute of the other device
> > > > >
> > > > > The string read from migration_version attribute is defined by device
> > > > > vendor
> > > > > driver and is completely opaque to the userspace.
> > > > > for a Intel vGPU, string format can be defined like
> > > > > "parent device PCI ID" + "version of gvt driver" + "mdev type" +
> > > > > "aggregator count".
> > > > >
> > > > > for an NVMe VF connecting to a remote storage. it could be
> > > > > "PCI ID" + "driver version" + "configured remote storage URL"
> > > > >
> > > > > for a QAT VF, it may be
> > > > > "PCI ID" + "driver version" + "supported encryption set".
> > > > >
> > > > > (to avoid namespace confliction from each vendor, we may prefix a
> > > > > driver name to
> > > > > each migration_version string. e.g.
> > > > > i915-v1-8086-591d-i915-GVTg_V5_8-1)
> > >
> > > It's very strange to define it as opaque and then proceed to describe
> > > the contents of that opaque string. The point is that its contents
> > > are defined by the vendor driver to describe the device, driver version,
> > > and possibly metadata about the configuration of the device. One
> > > instance of a device might generate a different string from another.
> > > The string that a device produces is not necessarily the only string
> > > the vendor driver will accept, for example the driver might support
> > > backwards compatible migrations.
> >
> > (As I've said in the previous discussion, off one of the patch series)
> >
> > My view is it makes sense to have a half-way house on the opaqueness of
> > this string; I'd expect to have an ID and version that are human
> > readable, maybe a device ID/name that's human interpretable and then a
> > bunch of other cruft that maybe device/vendor/version specific.
> >
> > I'm thinking that we want to be able to report problems and include the
> > string and the user to be able to easily identify the device that was
> > complaining and notice a difference in versions, and perhaps also use
> > it in compatibility patterns to find compatible hosts; but that does
> > get tricky when it's a 'ask the device if it's compatible'.
>
> In the reply I just sent to Dan, I gave this example of what a
> "compatibility string" might look like represented as json:
>
> {
> "device_api": "vfio-pci",
> "vendor": "vendor-driver-name",
> "version": {
> "major": 0,
> "minor": 1
> },
> "vfio-pci": { // Based on above device_api
> "vendor": 0x1234, // Values for the exposed device
> "device": 0x5678,
> // Possibly further parameters for a more specific match
> },
> "mdev_attrs": [
> { "attribute0": "VALUE" }
> ]
> }
>
> Are you thinking that we might allow the vendor to include a vendor
> specific array where we'd simply require that both sides have matching
> fields and values? ie.
>
> "vendor_fields": [
> { "unknown_field0": "unknown_value0" },
> { "unknown_field1": "unknown_value1" },
> ]
>
> We could certainly make that part of the spec, but I can't really
> figure the value of it other than to severely restrict compatibility,
> which the vendor could already do via the version.major value. Maybe
> they'd want to put a build timestamp, random uuid, or source sha1 into
> such a field to make absolutely certain compatibility is only determined
> between identical builds? Thanks,
No, I'd mostly anticipated matching on the vendor and device and maybe a
version number for the bit the user specifies; I had assumed all that
'vendor cruft' was still mostly opaque; having said that, if it did
become a list of attributes like that (some of which were vendor
specific) that would make sense to me.
Dave
>
> Alex
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
- device compatibility interface for live migration with assigned devices, Yan Zhao, 2020/07/13
- Re: device compatibility interface for live migration with assigned devices, Alex Williamson, 2020/07/14
- Re: device compatibility interface for live migration with assigned devices, Dr. David Alan Gilbert, 2020/07/14
- Re: device compatibility interface for live migration with assigned devices, Alex Williamson, 2020/07/14
- Re: device compatibility interface for live migration with assigned devices,
Dr. David Alan Gilbert <=
- Re: device compatibility interface for live migration with assigned devices, Yan Zhao, 2020/07/15
- RE: device compatibility interface for live migration with assigned devices, Feng, Shaohe, 2020/07/15
- Re: device compatibility interface for live migration with assigned devices, Alex Xu, 2020/07/15
- Re: device compatibility interface for live migration with assigned devices, Alex Williamson, 2020/07/17
- Re: device compatibility interface for live migration with assigned devices, Dr. David Alan Gilbert, 2020/07/17
- Re: device compatibility interface for live migration with assigned devices, Alex Williamson, 2020/07/17
- Re: device compatibility interface for live migration with assigned devices, Alex Xu, 2020/07/15
- Re: device compatibility interface for live migration with assigned devices, Alex Williamson, 2020/07/17
- Re: device compatibility interface for live migration with assigned devices, Alex Xu, 2020/07/15
Re: device compatibility interface for live migration with assigned devices, Jason Wang, 2020/07/16