On 08/31/2013 12:45 PM, Qin Chuanyu wrote: > 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. Maybe we can just stop vhost_net in pre_save() and enable it in post_load()? Then no need to use enable the dirty logging of vhost_net. > > > Regards > Qin chuanyu > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
