Re: [Qemu-devel] [PATCH] virtio-net: remove virtio queues if the guest doesn't support multiqueue

[Jason Wang]

On 07/15/2015 03:13 PM, Wen Congyang wrote:
> On 07/15/2015 02:59 PM, Jason Wang wrote:
>>
>> On 07/15/2015 02:23 PM, Wen Congyang wrote:
>>> commit da51a335 adds all queues in .realize(). But if the
>>> guest doesn't support multiqueue, we forget to remove them. And
>>> we cannot handle the ctrl vq corretly. The guest will hang.
>>>
>>> Signed-off-by: Wen Congyang <address@hidden>
>> Thanks for the patch, some questions, see below.
>>
>>> ---
>>>  hw/net/virtio-net.c | 69 
>>> +++++++++++++++++++++++++++++++++++++++++------------
>>>  1 file changed, 54 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>>> index e3c2db3..658806a 100644
>>> --- a/hw/net/virtio-net.c
>>> +++ b/hw/net/virtio-net.c
>>> @@ -1306,9 +1306,62 @@ static void virtio_net_tx_bh(void *opaque)
>>>      }
>>>  }
>>>  
>>> +static void virtio_net_add_queue(VirtIONet *n, int index)
>>> +{
>>> +    VirtIODevice *vdev = VIRTIO_DEVICE(n);
>>> +
>>> +    n->vqs[index].rx_vq = virtio_add_queue(vdev, 256, 
>>> virtio_net_handle_rx);
>>> +    if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
>>> +        n->vqs[index].tx_vq =
>>> +            virtio_add_queue(vdev, 256, virtio_net_handle_tx_timer);
>>> +        n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
>>> +                                              virtio_net_tx_timer,
>>> +                                              &n->vqs[index]);
>>> +    } else {
>>> +        n->vqs[index].tx_vq =
>>> +            virtio_add_queue(vdev, 256, virtio_net_handle_tx_bh);
>>> +        n->vqs[index].tx_bh = qemu_bh_new(virtio_net_tx_bh, 
>>> &n->vqs[index]);
>>> +    }
>>> +
>>> +    n->vqs[index].tx_waiting = 0;
>>> +    n->vqs[index].n = n;
>>> +}
>>> +
>>> +static void virtio_net_change_num_queues(VirtIONet *n, int new_max_queues)
>>> +{
>>> +    VirtIODevice *vdev = VIRTIO_DEVICE(n);
>>> +    int old_num_queues = virtio_get_num_queues(vdev);
>>> +    int new_num_queues = new_max_queues * 2 + 1;
>>> +    int i;
>>> +
>>> +    assert(old_num_queues >= 3);
>>> +    assert(old_num_queues % 2 == 1);
>>> +
>>> +    if (old_num_queues == new_num_queues) {
>>> +        return;
>>> +    }
>>> +
>>> +    /* Remove ctrl_vq first */
>>> +    virtio_del_queue(vdev, old_num_queues - 1);
>> Why ctrl vq must be first to be deleted?
> It just make the codes clean. We always need to remove and add ctrl vq if
> old_num_queues != new_num_queues. We only enter one of the two loops.
>
>>> +
>>> +    for (i = new_num_queues - 1; i < old_num_queues - 1; i++) {
>>> +        virtio_del_queue(vdev, i);
>> Do we need to delete bh and timer also here?
> I think we should delete it too. Before commit da51a335, we only call
> virtio_del_queue(), so I forgot to do it.
>
> Thanks
> Wen Congyang

I believe we need this patch for 2.4. So could you please do this in V2?

Thanks
>
>>> +    }
>>> +
>>> +    for (i = old_num_queues - 1; i < new_num_queues - 1; i += 2) {
>>> +        virtio_net_add_queue(n, i / 2);
>>> +    }
>>> +
>>> +    /* add ctrl_vq last */
>>> +    n->ctrl_vq = virtio_add_queue(vdev, 64, virtio_net_handle_ctrl);
>>> +}
>>> +
>>>  static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue)
>>>  {
>>> +    int max = multiqueue ? n->max_queues : 1;
>>> +
>>>      n->multiqueue = multiqueue;
>>> +    virtio_net_change_num_queues(n, max);
>>>  
>>>      virtio_net_set_queues(n);
>>>  }
>>> @@ -1583,21 +1636,7 @@ static void virtio_net_device_realize(DeviceState 
>>> *dev, Error **errp)
>>>      }
>>>  
>>>      for (i = 0; i < n->max_queues; i++) {
>>> -        n->vqs[i].rx_vq = virtio_add_queue(vdev, 256, 
>>> virtio_net_handle_rx);
>>> -        if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
>>> -            n->vqs[i].tx_vq =
>>> -                virtio_add_queue(vdev, 256, virtio_net_handle_tx_timer);
>>> -            n->vqs[i].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
>>> -                                              virtio_net_tx_timer,
>>> -                                              &n->vqs[i]);
>>> -        } else {
>>> -            n->vqs[i].tx_vq =
>>> -                virtio_add_queue(vdev, 256, virtio_net_handle_tx_bh);
>>> -            n->vqs[i].tx_bh = qemu_bh_new(virtio_net_tx_bh, &n->vqs[i]);
>>> -        }
>>> -
>>> -        n->vqs[i].tx_waiting = 0;
>>> -        n->vqs[i].n = n;
>>> +        virtio_net_add_queue(n, i);
>>>      }
>>>  
>>>      n->ctrl_vq = virtio_add_queue(vdev, 64, virtio_net_handle_ctrl);
>> .
>>
>