Re: [Qemu-devel] [PATCH V3] vhost_net: start/stop guest notifiers properly

[Michael S. Tsirkin]

On Thu, Aug 21, 2014 at 03:42:53PM +0800, Zhangjie (HZ) wrote:
> On 2014/8/21 14:53, Jason Wang wrote:
> > On 08/21/2014 02:28 PM, Zhangjie (HZ) wrote:
> >> 
> >> After migration, vhost is not disabled, virtual nic became unreachable 
> >> because vhost is not awakened.
> >> By the logical of EVENT_IDX, virtio-net will not kick vhost again if the 
> >> used idx is not updated.
> >> So, if one interrupts is lost during migration, virtio_net will not kick 
> >> vhost again.
> >> Then, no skb from virtio-net can be sent to tap.
> > 
> > Yes and I mean to test vhost=off to see if it was the issue of vhost.
> That sounds reasonable, but the test case is to test vhost.
> >>
> >> Jason's patch reduced the probability of occurrence, from about 1/20 to 
> >> 1/80. It is really effective. I think the patch should be acked.
> >> May be we can try to solve the problem from another perspective. Do you 
> >> have some methods to sense the migration?
> >> We can make up a signal from virtio-net after the migration.
> > 
> > You can make a patch like this to debug. If problem disappears, it means
> > interrupt was really lost anyway.
> >>
> >>> Anyway, I will try to reproduce it by myself.
> >>>
> >> The test environment is really terrible, I build a environment myself, but 
> >> it problem did not occur.
> >> The environment I use now is from a colleague Responsible for test work.
> >> Two hosts, every host has about 20 vms, they send packages(ipv4 and ipv6) 
> >> between each other.
> >> The VM to be migrated also sens packages itself, and there is a ping(-i 
> >> 0.001) from another host to it.
> >> The physical nic is 1GE, connected through a internal nework.
> > 
> > Just want to confirm. For the problem did not occur, you mean with my
> > patch on top?
> > .
> > 
> I mean, with your patch, I have to test 80 times before it occurs, the 
> probability is reduced.

Could you please try to apply the patch
        [PATCH V4] net: Forbid dealing with packets when VM is not running
on top and see if this helps?

Thanks!

> -- 
> Best Wishes!
> Zhang Jie