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

[Michael S. Tsirkin]

On Fri, Aug 29, 2014 at 06:40:24PM +0800, Zhangjie (HZ) wrote:
> 
> 
> On 2014/8/27 20:59, Michael S. Tsirkin wrote:
> > 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
> > .
> > 
> Thanks! I will have a test.

Great, once you have the result of the two patches applied
together, please let us know on the list.


> -- 
> Best Wishes!
> Zhang Jie