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

[Zhangjie (HZ)]

On 2014/8/21 12:29, Jason Wang wrote:
> On 08/20/2014 05:23 PM, Zhangjie (HZ) wrote:
>> On 2014/8/19 12:56, Jason Wang wrote:
>>> commit a9f98bb5ebe6fb1869321dcc58e72041ae626ad8 vhost: multiqueue
>>  call it before setting
>>> Zhang Jie, please test this patch to see if it fixes the issue.
>>> +static void vhost_net_set_vq_index(struct vhost_net *net, int vq_index)
>>> +{
>>> +    net->dev.vq_index = vq_index;
>>> +}
>>                           int vq_index)
>>> ...
>> Because of vhost_net_set_vq_index, VM can be start successfully.
>> But, after about 80 times of migration under my environment, virtual nic 
>> became unreachable again.
>> When I use jprobe to notify tap, the virtual nic becomes reachable again. 
>> This shows that interrupts missing causes
>> the problem.
> 
> Thanks for the testing. A questions is can you reproduce this when vhost
> is disabled?
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.

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.

> 
> 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.

-- 
Best Wishes!
Zhang Jie