Subject: Re: Query: Is it possible to lose interrupts between vhost and virtio_net during migration?

From: Jason Wang <[email-masked]>
Date: Thu, 14 Aug 2014 16:52:40 +0800

On 08/07/2014 08:47 PM, Zhangjie (HZ) wrote:
> On 2014/8/5 20:14, Zhangjie (HZ) wrote:
>> On 2014/8/5 17:49, Michael S. Tsirkin wrote:
>>> On Tue, Aug 05, 2014 at 02:29:28PM +0800, Zhangjie (HZ) wrote:
>>>> Jason is right, the new order is not the cause of network unreachable.
>>>> Changing order seems not work. After about 40 times, the problem occurs again.
>>>> Maybe there is other hidden reasons for that.
>> I modified the code to change the order myself yesterday.
>> This result is about my code.
>>> To make sure, you tested the patch that I posted to list:
>>> "vhost_net: stop guest notifiers after backend"?
>>>
>>> Please confirm.
>>>
>> OK, I will test with your patch "vhost_net: stop guest notifiers after backend".
>>
> Unfortunately, after using the patch "vhost_net: stop guest notifiers after backend",
> Linux VMs stopt themselves a few minutes after they were started.
>> @@ -308,6 +308,12 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
>>         goto err;
>>     }
>>
>> +    r = k->set_guest_notifiers(qbus->parent, total_queues * 2, true);
>> +    if (r < 0) {
>> +        error_report("Error binding guest notifier: %d", -r);
>> +        goto err;
>> +    }
>> +
>>     for (i = 0; i < total_queues; i++) {
>>         r = vhost_net_start_one(get_vhost_net(ncs[i].peer), dev, i * 2);
>>
>> @@ -316,12 +322,6 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
>>         }
>>     }
>>
>> -    r = k->set_guest_notifiers(qbus->parent, total_queues * 2, true);
>> -    if (r < 0) {
>> -        error_report("Error binding guest notifier: %d", -r);
>> -        goto err;
>> -    }
>> -
>>     return 0;
> I wonder if k->set_guest_notifiers should be called after "hdev->started = true;" in vhost_dev_start.

Michael, can we just remove those assertions? Since you may want to set
guest notifiers before starting the backend.

Another question for virtio_pci_vector_poll(): why not using
msix_notify() instead of msix_set_pending(). If so, there's no need to
change the vhost_net_start() ?

Zhang Jie, is this a regression? If yes, could you please do a bisection
to find the first bad commit.

Thanks