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

[fengyd]

---------- Forwarded message ---------
From: fengyd <address@hidden>
Date: Tue, 16 Apr 2019 at 09:17
Subject: Re: [Qemu-devel] How live migration work for vhost-user
To: Dr. David Alan Gilbert <address@hidden>


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.

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

Thanks
Yafeng

On Mon, 15 Apr 2019 at 22:54, Dr. David Alan Gilbert <address@hidden>
wrote:

> * fengyd (address@hidden) 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 / address@hidden / Manchester, UK
>