Re: [Qemu-devel] Fwd: How live migration work for vhost-user

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* fengyd (fengyd81@gmail.com) wrote:
> ---------- Forwarded message ---------
> From: fengyd <fengyd81@gmail.com>
> Date: Tue, 16 Apr 2019 at 09:17
> Subject: Re: [Qemu-devel] How live migration work for vhost-user
> To: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> 
> Hi,
> 
> Any special feature needs to be supported on guest driver?
> Because it's OK for standard Linux VM, but not OK for our VM where virtio
> is  implemented by ourself.

I'm not sure; you do have to support that 'log' mechanism but I don't
know what else is needed.

> And with qemu-kvm-ev-2.6, live migration can work with our VM where virtio
> is  implemented by ourself.

2.6 is pretty old, so there's a lot of changes - not sure what's
relevant.

Dave

> Thanks
> Yafeng
> 
> On Mon, 15 Apr 2019 at 22:54, Dr. David Alan Gilbert <dgilbert@redhat.com>
> wrote:
> 
> > * fengyd (fengyd81@gmail.com) wrote:
> > > Hi,
> > >
> > > During live migration,  the folloing log can see in nova-compute.log in
> > my
> > > environment:
> > >  ERROR nova.virt.libvirt.driver [req-039a85e1-e7a1-4a63-bc6d-c4b9a044aab6
> > > 0cdab20dc79f4bc6ae5790e7b4a898ac 3363c319773549178acc67f32c78310e -
> > default
> > > default] [instance: 5ec719f4-1865-4afe-a207-3d9fae22c410] Live Migration
> > > failure: internal error: qemu unexpectedly closed the monitor:
> > > 2019-04-15T02:58:22.213897Z qemu-kvm: VQ 0
> > > size 0x100 < last_avail_idx 0x1e - used_idx 0x23
> > >
> > > It's OK for standard Linux VM, but not OK for our VM where virtio is
> > > implemented by ourself.
> > > KVM version as follow:
> > > qemu-kvm-common-ev-2.12.0-18.el7_6.3.1.x86_64
> > > qemu-kvm-ev-2.12.0-18.el7_6.3.1.x86_64
> > > libvirt-daemon-kvm-3.9.0-14.2.el7.centos.ncir.8.x86_64
> > >
> > > Do you know what's the difference between virtio and vhost-user during
> > > migration?
> > > The function virtio_load in Qemu is called for virtio and vhost-user
> > during
> > > migration.
> > > For virtio,  last_avail_idx  and used_idx are stored in Qemu, Qemu is
> > > responsible for updating their values accordingly
> > > For vhost-user, last_avail_idx  and used_idx are stored in vhost-user
> > app,
> > > eg. DPDK, not in Qemu?
> > > How does migration work for vhost-user?
> >
> > I don't know the details, but my understanding is that vhost-user
> > tells the vhost-user client about an area of 'log' memory, where the
> > vhost-user client must mark pages as dirty.
> >
> > In the qemu source, see docs/interop/vhost-user.txt and see
> > the VHOST_SET_LOG_BASE and VHOST_USER_SET_LOG_FD calls.
> >
> > If the client correctly marks the areas as dirty, then qemu
> > should resend those pages across.
> >
> >
> > Dave
> >
> > > Thanks in advance
> > > Yafeng
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> >
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK