Re: [Qemu-devel] [PATCH 5/7] vhost_net: move vhost_net_set_vq_index ahead at vhost_net_init

[Jason Wang <jasowang@redhat.com>]

On 09/10/2015 01:17 PM, Yuanhan Liu wrote:
> On Thu, Sep 10, 2015 at 12:46:00PM +0800, Jason Wang wrote:
>> > 
>> > 
>> > On 09/10/2015 11:57 AM, Yuanhan Liu wrote:
>>> > > On Thu, Sep 10, 2015 at 11:14:27AM +0800, Jason Wang wrote:
>>>> > >>
>>>> > >> On 09/08/2015 03:38 PM, Yuanhan Liu wrote:
>>>>> > >>> So that we could use the `vq_index' as well in the vhost_net_init
>>>>> > >>> stage, which is required when adding vhost-user multiple-queue support,
>>>>> > >>> where we need the vq_index to indicate which queue pair we are gonna
>>>>> > >>> initiate.
>>>>> > >>>
>>>>> > >>> vhost-user has no multiple queue support yet, hence no queue_index set
>>>>> > >>> before. Here is a quick set to 0 at net_vhost_user_init() stage, and it
>>>>> > >>> will be set properly soon in the next patch.
>>>>> > >>>
>>>>> > >>> Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
>>>>> > >>> ---
>>>>> > >>>  hw/net/vhost_net.c | 16 +++++++---------
>>>>> > >>>  net/vhost-user.c   |  1 +
>>>>> > >>>  2 files changed, 8 insertions(+), 9 deletions(-)
>>>>> > >>>
>>>>> > >>> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
>>>>> > >>> index f9441e9..141b557 100644
>>>>> > >>> --- a/hw/net/vhost_net.c
>>>>> > >>> +++ b/hw/net/vhost_net.c
>>>>> > >>> @@ -138,6 +138,11 @@ static int vhost_net_get_fd(NetClientState *backend)
>>>>> > >>>      }
>>>>> > >>>  }
>>>>> > >>>  
>>>>> > >>> +static void vhost_net_set_vq_index(struct vhost_net *net, int vq_index)
>>>>> > >>> +{
>>>>> > >>> +    net->dev.vq_index = vq_index;
>>>>> > >>> +}
>>>>> > >>> +
>>>>> > >>>  struct vhost_net *vhost_net_init(VhostNetOptions *options)
>>>>> > >>>  {
>>>>> > >>>      int r;
>>>>> > >>> @@ -167,6 +172,8 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
>>>>> > >>>      }
>>>>> > >>>      net->nc = options->net_backend;
>>>>> > >>>  
>>>>> > >>> +    vhost_net_set_vq_index(net, net->nc->queue_index * 2);
>>>>> > >>> +
>>>> > >> This breaks vhost kernel multiqueue since queue_index was not
>>>> > >> initialized at this time.
>>> > > Right, thanks for pointing it out.
>>> > >
>>>> > >> We do this in set_netdev() instead of setting
>>>> > >> it in each kind of netdev.
>>> > > Can we move it to net_init_tap() for setting the right queue_index
>>> > > for each nc?
>>> > >
>>> > > Or, can we call vhost_net_set_vq_index twice, one at vhost_net_init(for
>>> > > vhost-user mq support), another one at vhost_net_start(for vhost kernel
>>> > > mq support)?
>>> > >
>>> > > Or, do you have better ideas?
>> > 
>> > I think setting queue_index in net_init_tap() looks ok.
> Good to know.
>
>> > But a question
>> > is that why need we do this at so early stage? ( Even before its peers
>> > is connected.)
> For vhost-user multiple queues support, we will invoke vhost_net_init()
> N times for each queue pair, and hence we need to distinguish which
> queue it is while sending messages like VHOST_SET_VRING_CALL for
> initializing corresponding queue pair.
>
> Does that make sense to you?
>

Not sure. Since current codes works for vhost-kernel. (vhost_net_init()
was also called N times). We don't want to break existed vhost-kernel
API when developing multiqueue. For each virtqueue TX/RX pair, we have
one vhost net device and it has no knowledge for the others (which was
hide by qemu). So VHOST_SET_VRING_CALL works without any change here.

For the case here, since you still have multiple instances of vhost_net
structure. Maybe the vhost-user backend can distinguish form this?