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

[Jason Wang]

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 <address@hidden>
>>> ---
>>>  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. But a question
is that why need we do this at so early stage? ( Even before its peers
is connected.)

>
>>>      net->dev.nvqs = 2;
>>>      net->dev.vqs = net->vqs;
>>>  
>>> @@ -196,11 +203,6 @@ fail:
>>>      return NULL;
>>>  }
>>>  
>>> -static void vhost_net_set_vq_index(struct vhost_net *net, int vq_index)
>>> -{
>>> -    net->dev.vq_index = vq_index;
>>> -}
>>> -
>>>  static int vhost_net_set_vnet_endian(VirtIODevice *dev, NetClientState 
>>> *peer,
>>>                                       bool set)
>>>  {
>>> @@ -325,10 +327,6 @@ int vhost_net_start(VirtIODevice *dev, NetClientState 
>>> *ncs,
>>>          goto err;
>>>      }
>>>  
>>> -    for (i = 0; i < total_queues; i++) {
>>> -        vhost_net_set_vq_index(get_vhost_net(ncs[i].peer), i * 2);
>>> -    }
>>> -
>>>      r = k->set_guest_notifiers(qbus->parent, total_queues * 2, true);
>>>      if (r < 0) {
>>>          error_report("Error binding guest notifier: %d", -r);
>>> diff --git a/net/vhost-user.c b/net/vhost-user.c
>>> index 93dcecd..2d6bbe5 100644
>>> --- a/net/vhost-user.c
>>> +++ b/net/vhost-user.c
>>> @@ -146,6 +146,7 @@ static int net_vhost_user_init(NetClientState *peer, 
>>> const char *device,
>>>      /* We don't provide a receive callback */
>>>      s->nc.receive_disabled = 1;
>>>      s->chr = chr;
>>> +    nc->queue_index = 0;
>>>  
>> Fail to understand why this is needed. It will be set to correct value
>> in set_netdev().
> Right, it's unnecessary.
>
> BTW, May I ask you a quick question: why set_netdev is invoked after
> tap init, while it is invoked before vhost-user init?
>
>       --yliu

I think the reason is that you must initialize all netdevs before a
device tries to connect them.

>>>      qemu_chr_add_handlers(s->chr, NULL, NULL, net_vhost_user_event, s);
>>>