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Date: Wed, 17 Nov 2010 22:49:52 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [Qemu-devel] Re: [PATCH v4 0/4] virtio: Use ioeventfd for
	virtqueue notify
Message-ID: <20101117204952.GA31717@redhat.com>
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On Wed, Nov 17, 2010 at 08:38:25PM +0000, Stefan Hajnoczi wrote:
> On Wed, Nov 17, 2010 at 6:01 PM, Michael S. Tsirkin <mst@redhat.com> wr=
ote:
> > On Wed, Nov 17, 2010 at 04:19:25PM +0000, Stefan Hajnoczi wrote:
> >> The v4 version includes:
> >> =A0* Simpler start/stop ioeventfd mechanism using bool ioeventfd_sta=
rted state
> >> =A0* Support for migration
> >> =A0* Handle deassign race condition to avoid dropping a virtqueue ki=
ck
> >> =A0* Add missing kvm_enabled() check to kvm_has_many_ioeventfds()
> >> =A0* Documentation updates for qdev -device with ioeventfd=3Don|off
> >
> > Anthony, could you pls remind me what did you say
> > about need to stop these threads on migration vmstop?
> > Or am I confusing this with something else?
>=20
> Two points about the VM change state:
> 1. It is used to bring up virtio-ioeventfd on the destination host
> after migration.
> 2. It handles the race condition where a virtqueue kick is dropped
> because we deassign the ioeventfd on the source host.
>=20
> So I've implemented the VM change state to get correct migration behavi=
or.
>=20
> The discussion you had with Anthony was more about events happening
> while the VM is paused and how that could interfere with guest state
> for migration IIRC.
>=20
> Stefan

Exactly. Could your patches cause a situation where block virtio ring
is used after migration stopped a VM?

--=20
MST