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Date: Thu, 31 Jul 2014 16:31:00 +0200 From: "Michael S. Tsirkin" <mst@...hat.com> To: "Zhangjie (HZ)" <zhangjie14@...wei.com> Cc: netdev@...r.kernel.org, jasowang@...hat.com, qinchuanyu@...wei.com, liuyongan@...wei.com, davem@...emloft.net Subject: Re: Query: Is it possible to lose interrupts between vhost and virtio_net during migration? On Thu, Jul 31, 2014 at 07:47:24PM +0800, Zhangjie (HZ) wrote: > [The test scenario]: > > Doing migration between two Hosts roundly(A->B, B->A) ,after about 20 times, network of the VM is unreachable. > There are other 20 VMs in each Host, and they send ipv4 or ipv6 and multicast packets to each other. > Sometimes the CPU idle of the Host maybe 0; > > [Problem description]: > > I wonder if it was interrupts missing that cause the network unreachable. > In the migration process of kvm, source end should suspend, which include steps as follows: > 1. do_vm_stop->pause_all_vcpus > 2. vm_state_notify-> vhost_net_stop->set_guest_notifiers->kvm_virtio_pci_vq_vector_release > 3. vm_state_notify-> vhost_net_stop-> vhost_net_stop_one->OST_NET_SET_BACKEND-> vhost_net_flush_vq-> vhost_work_flush > This may cause interrupts missing. Supose the scene that, virtqueue_notify() is called in virtio_net, > then the VM is paused. And, just before the portiowrite being handled, eventfd of kvm is released. > Then, vhost could not sense the notify, and the tx notify is lost. > On the other side, if eventfd of kvm is released just after vhost_notify(), and before eventfd_signal(), then rx signal by vhost is lost. Could be a bug in userspace: should should cleanups notifiers after it stops vhost. Could you please send this to appropriate mailing lists? I have a policy against off-list discussions. -- MST -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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