Qin Chuanyu
2013-Aug-31 04:45 UTC
Re: Is fallback vhost_net to qemu for live migrate available?
On 2013/8/30 0:08, Anthony Liguori wrote:> Hi Qin,>> By change the memory copy and notify mechanism ,currently virtio-net with >> vhost_net could run on Xen with good performance。 > > I think the key in doing this would be to implement a property > ioeventfd and irqfd interface in the driver domain kernel. Just > hacking vhost_net with Xen specific knowledge would be pretty nasty > IMHO. >Yes, I add a kernel module which persist virtio-net pio_addr and msix address as what kvm module did. Guest wake up vhost thread by adding a hook func in evtchn_interrupt.> Did you modify the front end driver to do grant table mapping or is > this all being done by mapping the domain's memory? >There is nothing changed in front end driver. Currently I use alloc_vm_area to get address space, and map the domain's memory as what what qemu did.> KVM and Xen represent memory in a very different way. KVM can only > track when guest mode code dirties memory. It relies on QEMU to track > when guest memory is dirtied by QEMU. Since vhost is running outside > of QEMU, vhost also needs to tell QEMU when it has dirtied memory. > > I don't think this is a problem with Xen though. I believe (although > could be wrong) that Xen is able to track when either the domain or > dom0 dirties memory. > > So I think you can simply ignore the dirty logging with vhost and it > should Just Work. >Thanks for your advice, I have tried it, without ping, it could migrate successfully, but if there has skb been received, domU would crash. I guess that because though Xen track domU memory, but it could only track memory that changed in DomU. memory changed by Dom0 is out of control.> > No, we don't have a mechanism to fallback to QEMU for the datapath. > It would be possible but I think it's a bad idea to mix and match the > two. >Next I would try to fallback datapath to qemu for three reason: 1: memory translate mechanism has been changed for vhost_net on Xen,so there would be some necessary changed needed for vhost_log in kernel. 2: I also maped IOREQ_PFN page(which is used for communication between qemu and Xen) in kernel notify module, so it also needed been marked as dirty when tx/rx exist in migrate period. 3: Most important of all, Michael S. Tsirkin said that he hadn't considered about vhost_net migrate on Xen,so there would be some changed needed in vhost_log for qemu. fallback to qemu seems to much easier, isn't it. Regards Qin chuanyu _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel