On Tue, Aug 27, 2013 at 03:04:54PM +0800, Qin Chuanyu wrote:

On 2013/8/27 12:19, Michael S. Tsirkin wrote:

quoted

On Tue, Aug 27, 2013 at 11:32:31AM +0800, Qin Chuanyu wrote:

quoted

Hi all

I am participating in a project which try to port vhost_net on Xen。

By change the memory copy and notify mechanism ，currently
virtio-net with vhost_net could run on Xen with good
performance。TCP receive throughput of single vnic from 2.77Gbps up
to 6Gps。In VM receive side，I instead grant_copy with grant_map +
memcopy，it efficiently reduce the cost of grant_table spin_lock of
dom0，So the hole server TCP performance from 5.33Gps up to 9.5Gps。

Now I am consider the live migrate of vhost_net on Xen，vhost_net
use vhost_log for live migrate on Kvm，but qemu on Xen havn't manage
the hole memory of VM，So I am trying to fallback datapath from
vhost_net to qemu when doing live migrate ，and fallback datapath
from qemu to
vhost_net again after vm migrate to new server。

My question is：
why didn't vhost_net do the same fallback operation for live
migrate on KVM，but use vhost_log to mark the dirty page？
Is there any mechanism fault for the idea of fallback datapath from
vhost_net to qemu for live migrate？

any question about the detail of vhost_net on Xen is welcome。

Thanks

It should work, in practice.

However, one issue with this approach that I see is that you
are running two instances of virtio-net on the host:
qemu and vhost-net, doubling your security surface
for guest to host attack.

I don't exactly see why does it matter that qemu doesn't manage
the whole memory of a VM - vhost only needs to log
memory writes that it performs.


.

Thanks for your reply.

In fact，I am not sure that whether vhost_log could work on Xen live
migrate or not. Yes，vhost_sync_dirty_bitmap work well on Kvm，but
vhost_net havn't run on Xen before，although the method
vhost_dev_sync_region -> memory_region_set_dirty ->
xen_modified_memory call sequence exist.

Have you considered the scene that vhost_migration_log code running
on Xen？ If yes，it sames much easier then fallback datapath from
vhost_net to qemu for live migrate.

I never looked at how Xen live migration works with QEMU so I don't
know.