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

[Jason Wang <jasowang@redhat.com>]

On 03/04/2014 11:26 AM, Gonglei (Arei) wrote:
>> -----Original Message-----
>> From: qemu-devel-bounces+arei.gonglei=huawei.com@nongnu.org
>> [mailto:qemu-devel-bounces+arei.gonglei=huawei.com@nongnu.org] On
>> Behalf Of Jason Wang
>> Sent: Friday, February 21, 2014 5:05 PM
>> To: aliguori@amazon.com; mst@redhat.com; qemu-devel@nongnu.org
>> 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 <pbonzini@redhat.com>
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>  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 <arei.gonglei@huawei.com>
>
>
> 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.