From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: kvm@vger.kernel.org, libvir-list@redhat.com,
Jason Wang <jasowang@redhat.com>,
qemu-devel@nongnu.org, 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, Yan Zhao <yan.y.zhao@intel.com>,
eskultet@redhat.com, jian-feng.ding@intel.com,
zhenyuw@linux.intel.com, hejie.xu@intel.com,
bao.yumeng@zte.com.cn, smooney@redhat.com,
intel-gvt-dev@lists.freedesktop.org, berrange@redhat.com,
cohuck@redhat.com, dinechin@redhat.com, devel@ovirt.org
Subject: Re: device compatibility interface for live migration with assigned devices
Date: Wed, 29 Jul 2020 20:05:41 +0100 [thread overview]
Message-ID: <20200729190540.GK2795@work-vm> (raw)
In-Reply-To: <20200727162321.7097070e@x1.home>
* Alex Williamson (alex.williamson@redhat.com) wrote:
> On Mon, 27 Jul 2020 15:24:40 +0800
> Yan Zhao <yan.y.zhao@intel.com> wrote:
>
> > > > As you indicate, the vendor driver is responsible for checking version
> > > > information embedded within the migration stream. Therefore a
> > > > migration should fail early if the devices are incompatible. Is it
> > > but as I know, currently in VFIO migration protocol, we have no way to
> > > get vendor specific compatibility checking string in migration setup stage
> > > (i.e. .save_setup stage) before the device is set to _SAVING state.
> > > In this way, for devices who does not save device data in precopy stage,
> > > the migration compatibility checking is as late as in stop-and-copy
> > > stage, which is too late.
> > > do you think we need to add the getting/checking of vendor specific
> > > compatibility string early in save_setup stage?
> > >
> > hi Alex,
> > after an offline discussion with Kevin, I realized that it may not be a
> > problem if migration compatibility check in vendor driver occurs late in
> > stop-and-copy phase for some devices, because if we report device
> > compatibility attributes clearly in an interface, the chances for
> > libvirt/openstack to make a wrong decision is little.
>
> I think it would be wise for a vendor driver to implement a pre-copy
> phase, even if only to send version information and verify it at the
> target. Deciding you have no device state to send during pre-copy does
> not mean your vendor driver needs to opt-out of the pre-copy phase
> entirely. Please also note that pre-copy is at the user's discretion,
> we've defined that we can enter stop-and-copy at any point, including
> without a pre-copy phase, so I would recommend that vendor drivers
> validate compatibility at the start of both the pre-copy and the
> stop-and-copy phases.
That's quite curious; from a migration point of view I'd expect if you
did want to skip pre-copy, that you'd go through the motions of entering
it and then not saving any data and then going to stop-and-copy,
rather than having two flows.
Note that failing at a late stage of stop-and-copy is a pain; if you've
just spent an hour migrating your huge busy VM over, you're going to be
pretty annoyed when it goes pop near the end.
Dave
> > so, do you think we are now arriving at an agreement that we'll give up
> > the read-and-test scheme and start to defining one interface (perhaps in
> > json format), from which libvirt/openstack is able to parse and find out
> > compatibility list of a source mdev/physical device?
>
> Based on the feedback we've received, the previously proposed interface
> is not viable. I think there's agreement that the user needs to be
> able to parse and interpret the version information. Using json seems
> viable, but I don't know if it's the best option. Is there any
> precedent of markup strings returned via sysfs we could follow?
>
> Your idea of having both a "self" object and an array of "compatible"
> objects is perhaps something we can build on, but we must not assume
> PCI devices at the root level of the object. Providing both the
> mdev-type and the driver is a bit redundant, since the former includes
> the latter. We can't have vendor specific versioning schemes though,
> ie. gvt-version. We need to agree on a common scheme and decide which
> fields the version is relative to, ex. just the mdev type?
>
> I had also proposed fields that provide information to create a
> compatible type, for example to create a type_x2 device from a type_x1
> mdev type, they need to know to apply an aggregation attribute. If we
> need to explicitly list every aggregation value and the resulting type,
> I think we run aground of what aggregation was trying to avoid anyway,
> so we might need to pick a language that defines variable substitution
> or some kind of tagging. For example if we could define ${aggr} as an
> integer within a specified range, then we might be able to define a type
> relative to that value (type_x${aggr}) which requires an aggregation
> attribute using the same value. I dunno, just spit balling. Thanks,
>
> Alex
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
prev parent reply other threads:[~2020-07-29 19:06 UTC|newest]
Thread overview: 118+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-13 23:29 device compatibility interface for live migration with assigned devices Yan Zhao
2020-07-14 10:21 ` Daniel P. Berrangé
2020-07-14 12:33 ` Sean Mooney
[not found] ` <20200714110148.0471c03c@x1.home>
[not found] ` <eb705c72cdc8b6b8959b6ebaeeac6069a718d524.camel@redhat.com>
2020-07-14 21:15 ` Sean Mooney
2020-07-14 16:16 ` Alex Williamson
2020-07-14 16:47 ` Daniel P. Berrangé
2020-07-14 20:47 ` Alex Williamson
2020-07-15 9:16 ` Daniel P. Berrangé
2020-07-14 17:19 ` Dr. David Alan Gilbert
2020-07-14 20:59 ` Alex Williamson
2020-07-15 7:37 ` Alex Xu
2020-07-17 15:18 ` Alex Williamson
2020-07-15 8:20 ` Yan Zhao
2020-07-15 8:49 ` Feng, Shaohe
2020-07-15 9:21 ` Alex Xu
2020-07-17 14:59 ` Alex Williamson
2020-07-17 18:03 ` Dr. David Alan Gilbert
2020-07-17 18:30 ` Alex Williamson
2020-07-15 8:23 ` Dr. David Alan Gilbert
2020-07-15 7:23 ` Alex Xu
2020-07-16 4:16 ` Jason Wang
2020-07-16 8:32 ` Yan Zhao
2020-07-16 9:30 ` Jason Wang
2020-07-17 16:12 ` Alex Williamson
2020-07-20 3:41 ` Jason Wang
2020-07-20 10:39 ` Sean Mooney
2020-07-21 2:11 ` Jason Wang
2020-07-21 0:51 ` Yan Zhao
2020-07-27 7:24 ` Yan Zhao
2020-07-27 22:23 ` Alex Williamson
2020-07-29 8:05 ` Yan Zhao
2020-07-29 11:28 ` Sean Mooney
2020-07-29 19:12 ` Alex Williamson
2020-07-30 3:41 ` Yan Zhao
2020-07-30 13:24 ` Sean Mooney
2020-07-30 17:29 ` Alex Williamson
2020-08-04 8:37 ` Yan Zhao
2020-08-05 9:44 ` Dr. David Alan Gilbert
2020-07-30 1:56 ` Yan Zhao
2020-07-30 13:14 ` Sean Mooney
2020-08-04 16:35 ` Cornelia Huck
2020-08-05 2:22 ` Jason Wang
2020-08-05 2:16 ` Yan Zhao
2020-08-05 2:41 ` Jason Wang
2020-08-05 7:56 ` Jiri Pirko
2020-08-05 8:02 ` Jason Wang
2020-08-05 9:33 ` Yan Zhao
2020-08-05 10:53 ` Jiri Pirko
2020-08-05 11:35 ` Sean Mooney
2020-08-07 11:59 ` Cornelia Huck
2020-08-13 15:33 ` Cornelia Huck
2020-08-13 19:02 ` Eric Farman
2020-08-17 6:38 ` Cornelia Huck
2020-08-10 7:46 ` Yan Zhao
2020-08-13 4:24 ` Jason Wang
2020-08-14 5:16 ` Yan Zhao
2020-08-14 12:30 ` Sean Mooney
2020-08-17 1:52 ` Yan Zhao
2020-08-18 3:24 ` Jason Wang
2020-08-18 8:55 ` Daniel P. Berrangé
2020-08-18 9:06 ` Cornelia Huck
2020-08-18 9:24 ` Daniel P. Berrangé
2020-08-18 9:38 ` Cornelia Huck
[not found] ` <3a073222-dcfe-c02d-198b-29f6a507b2e1@redhat.com>
2020-08-18 9:16 ` Daniel P. Berrangé
2020-08-18 9:36 ` Cornelia Huck
2020-08-18 9:39 ` Parav Pandit
2020-08-19 3:30 ` Yan Zhao
2020-08-19 5:58 ` Parav Pandit
2020-08-19 9:41 ` Jason Wang
2020-08-19 6:57 ` [ovirt-devel] " Jason Wang
2020-08-19 6:59 ` Yan Zhao
2020-08-19 7:39 ` Jason Wang
2020-08-19 8:13 ` Yan Zhao
2020-08-19 9:28 ` Jason Wang
2020-08-20 12:27 ` Cornelia Huck
2020-08-21 3:14 ` Jason Wang
2020-08-21 14:52 ` Cornelia Huck
2020-08-31 3:07 ` Jason Wang
2020-08-19 17:50 ` Alex Williamson
2020-08-20 0:18 ` Yan Zhao
2020-08-20 3:13 ` Alex Williamson
2020-08-20 3:09 ` Yan Zhao
2020-08-19 2:54 ` Jason Wang
2020-08-20 0:39 ` Yan Zhao
2020-08-20 1:29 ` Sean Mooney
2020-08-20 4:01 ` Yan Zhao
2020-08-20 5:16 ` Sean Mooney
2020-08-20 6:27 ` Yan Zhao
2020-08-20 13:24 ` Sean Mooney
2020-08-26 8:54 ` Yan Zhao
2020-08-20 3:22 ` Alex Williamson
2020-08-20 3:16 ` Yan Zhao
2020-08-25 14:39 ` Cornelia Huck
2020-08-26 6:41 ` Yan Zhao
2020-08-28 13:47 ` Cornelia Huck
2020-08-28 14:04 ` Sean Mooney
2020-08-31 4:43 ` Yan Zhao
2020-09-08 14:41 ` Cornelia Huck
2020-09-09 2:13 ` Yan Zhao
2020-09-10 12:38 ` Cornelia Huck
2020-09-10 12:50 ` Sean Mooney
2020-09-10 18:02 ` Alex Williamson
2020-09-11 0:56 ` Yan Zhao
2020-09-11 10:08 ` Cornelia Huck
2020-09-11 10:18 ` Tian, Kevin
2020-09-11 16:51 ` Alex Williamson
2020-09-14 13:48 ` Zeng, Xin
2020-09-14 14:44 ` Alex Williamson
2020-09-15 7:46 ` Zeng, Xin
2020-09-09 5:37 ` Yan Zhao
2020-08-31 2:23 ` Yan Zhao
2020-08-19 2:38 ` Jason Wang
2020-08-18 9:32 ` Parav Pandit
2020-08-19 2:45 ` Jason Wang
2020-08-19 5:26 ` Parav Pandit
2020-08-19 6:48 ` Jason Wang
2020-08-19 6:53 ` Parav Pandit
2020-07-29 19:05 ` Dr. David Alan Gilbert [this message]
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