From: "Michael S. Tsirkin" <mst@redhat.com>
To: "Zhangjie (HZ)" <zhangjie14@huawei.com>
Cc: netdev@vger.kernel.org, jasowang@redhat.com,
qinchuanyu@huawei.com, liuyongan@huawei.com, davem@davemloft.net
Subject: Re: Query: Is it possible to lose interrupts between vhost and virtio_net during migration?
Date: Thu, 31 Jul 2014 16:37:25 +0200 [thread overview]
Message-ID: <20140731143725.GA3875@redhat.com> (raw)
In-Reply-To: <20140731143100.GA3834@redhat.com>
On Thu, Jul 31, 2014 at 04:31:00PM +0200, Michael S. Tsirkin wrote:
> 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.
Also, Jason, could you take a look please?
Looks like your patch a9f98bb5ebe6fb1869321dcc58e72041ae626ad8
changed the order of stopping the device.
Previously vhost_dev_stop would disable backend and only afterwards,
unset guest notifiers. You now unset guest notifiers while vhost is still
active. Looks like this can lose events?
> --
> MST
next prev parent reply other threads:[~2014-07-31 14:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-31 11:47 Query: Is it possible to lose interrupts between vhost and virtio_net during migration? Zhangjie (HZ)
2014-07-31 14:31 ` Michael S. Tsirkin
2014-07-31 14:37 ` Michael S. Tsirkin [this message]
2014-08-01 10:47 ` Jason Wang
2014-08-01 11:14 ` Jason Wang
2014-08-05 6:29 ` Zhangjie (HZ)
2014-08-05 9:49 ` Michael S. Tsirkin
2014-08-05 12:14 ` Zhangjie (HZ)
2014-08-07 12:47 ` Zhangjie (HZ)
2014-08-14 8:52 ` Jason Wang
2014-08-14 10:02 ` Michael S. Tsirkin
2014-08-15 2:55 ` Jason Wang
2014-08-17 10:22 ` Michael S. Tsirkin
2014-08-18 5:23 ` Jason Wang
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