Re: [Qemu-devel] [PATCH V2] virtio-net: calculate proper msix vectors on init

[Gonglei]

On 2014/3/4 15:41, Jason Wang wrote:

> On 03/04/2014 11:26 AM, Gonglei (Arei) wrote:
>>> -----Original Message-----
>>> From: address@hidden
>>> [mailto:address@hidden On
>>> Behalf Of Jason Wang
>>> Sent: Friday, February 21, 2014 5:05 PM
>>> To: address@hidden; address@hidden; address@hidden
>>> Cc: Paolo Bonzini; Jason Wang
>>> Subject: [Qemu-devel] [PATCH V2] virtio-net: calculate proper msix vectors 
>>> on
>>> init
>>>
>>> Currently, the default msix vectors for virtio-net-pci is 3 which is
>>> obvious not suitable for multiqueue guest, so we depends on the user
>>> or management tools to pass a correct vectors parameter. In fact, we
>>> can simplifying this by calculate the number of vectors on init.
>>>
>>> Consider we have N queues, the number of vectors needed is 2*N + 2
>>> (plus one config interrupt and control vq). We didn't check whether or
>>> not host support control vq because it was added unconditionally by
>>> qemu to avoid breaking legacy guests such as Minix.
>>>
>>> Cc: Paolo Bonzini <address@hidden>
>>> Cc: Michael S. Tsirkin <address@hidden>
>>> Signed-off-by: Jason Wang <address@hidden>
>>> ---
>>>  hw/virtio/virtio-pci.c | 8 +++++++-
>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
>>> index 7b91841..3b3b0e2 100644
>>> --- a/hw/virtio/virtio-pci.c
>>> +++ b/hw/virtio/virtio-pci.c
>>> @@ -1416,7 +1416,8 @@ static const TypeInfo virtio_serial_pci_info = {
>>>  static Property virtio_net_properties[] = {
>>>      DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
>>>                      VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, false),
>>> -    DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 3),
>>> +    DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors,
>>> +                       DEV_NVECTORS_UNSPECIFIED),
>>>      DEFINE_VIRTIO_NET_FEATURES(VirtIOPCIProxy, host_features),
>>>      DEFINE_NIC_PROPERTIES(VirtIONetPCI, vdev.nic_conf),
>>>      DEFINE_VIRTIO_NET_PROPERTIES(VirtIONetPCI, vdev.net_conf),
>>> @@ -1428,6 +1429,11 @@ static int virtio_net_pci_init(VirtIOPCIProxy
>>> *vpci_dev)
>>>      DeviceState *qdev = DEVICE(vpci_dev);
>>>      VirtIONetPCI *dev = VIRTIO_NET_PCI(vpci_dev);
>>>      DeviceState *vdev = DEVICE(&dev->vdev);
>>> +    VirtIONet *net = VIRTIO_NET(&dev->vdev);
>>> +
>>> +    if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
>>> +        vpci_dev->nvectors = 2 * MAX(net->nic_conf.queues, 1) + 2;
>>> +    }
>>>
>>>      virtio_net_set_config_size(&dev->vdev, vpci_dev->host_features);
>>>      virtio_net_set_netclient_name(&dev->vdev, qdev->id,
>>> --
>>> 1.8.3.2
>>>
>> Good catch.
>>
>> Reviewed-by: Gonglei <address@hidden>
>>
>>
>> Best regards,
>> -Gonglei
>>
> 
> Hi Gonglei:
> 
> Thanks for the reviewing. Looks like this patch has a bug which will
> break the migration if "vectors=" is not specified.
> 
> Will post a new version.
> 


Yes, you are right, Jason.
You need to add backwards-compatibility properties in hw/pc.h

Best regards,
-Gonglei