netdev - Re: [RFC PATCH net-next v5 3/4] virtio_net: Extend virtio to use VF datapath when available

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Message-ID: <2ccfad76-589d-9dca-7e4b-9bafee41f844@intel.com>
Date:   Tue, 10 Apr 2018 08:13:40 -0700
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     mst@...hat.com, stephen@...workplumber.org, davem@...emloft.net,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, jesse.brandeburg@...el.com,
        alexander.h.duyck@...el.com, kubakici@...pl, jasowang@...hat.com,
        loseweigh@...il.com
Subject: Re: [RFC PATCH net-next v5 3/4] virtio_net: Extend virtio to use VF
 datapath when available

On 4/10/2018 3:55 AM, Jiri Pirko wrote:
> Mon, Apr 09, 2018 at 08:47:06PM CEST, sridhar.samudrala@...el.com wrote:
>> On 4/9/2018 1:07 AM, Jiri Pirko wrote:
>>> Sat, Apr 07, 2018 at 12:59:14AM CEST, sridhar.samudrala@...el.com wrote:
>>>> On 4/6/2018 5:48 AM, Jiri Pirko wrote:
>>>>> Thu, Apr 05, 2018 at 11:08:22PM CEST, sridhar.samudrala@...el.com wrote:
>>> [...]
>>>
>>>>>> +static int virtnet_bypass_join_child(struct net_device *bypass_netdev,
>>>>>> +				     struct net_device *child_netdev)
>>>>>> +{
>>>>>> +	struct virtnet_bypass_info *vbi;
>>>>>> +	bool backup;
>>>>>> +
>>>>>> +	vbi = netdev_priv(bypass_netdev);
>>>>>> +	backup = (child_netdev->dev.parent == bypass_netdev->dev.parent);
>>>>>> +	if (backup ? rtnl_dereference(vbi->backup_netdev) :
>>>>>> +			rtnl_dereference(vbi->active_netdev)) {
>>>>>> +		netdev_info(bypass_netdev,
>>>>>> +			    "%s attempting to join bypass dev when %s already present\n",
>>>>>> +			    child_netdev->name, backup ? "backup" : "active");
>>>>> Bypass module should check if there is already some other netdev
>>>>> enslaved and refuse right there.
>>>> This will work for virtio-net with 3 netdev model, but this check has to be done by netvsc
>>>> as its bypass_netdev is same as the backup_netdev.
>>>> Will add a flag while registering with the bypass module to indicate if the driver is doing
>>>> a 2 netdev or 3 netdev model and based on that flag this check can be done in bypass module
>>>> for 3 netdev scenario.
>>> Just let me undestand it clearly. What I expect the difference would be
>>> between 2netdev and3 netdev model is this:
>>> 2netdev:
>>>     bypass_master
>>>        /
>>>       /
>>> VF_slave
>>>
>>> 3netdev:
>>>     bypass_master
>>>        /     \
>>>       /       \
>>> VF_slave   backup_slave
>>>
>>> Is that correct? If not, how does it look like?
>>>
>>>
>> Looks correct.
>> VF_slave and backup_slave are the original netdevs and are present in both the models.
>> In the 3 netdev model, bypass_master netdev is created and VF_slave and backup_slave are
>> marked as the 2 slaves of this new netdev.
> You say it looks correct and in another sentence you provide completely
> different description. Could you please look again?
>
To be exact, 2 netdev model with netvsc looks like this.

     netvsc_netdev
       /
      /
  VF_slave

With virtio_net, 3 netdev model

   bypass_netdev
       /     \
      /       \
VF_slave   virtio_net netdev