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: <d08ed1e6-678a-7b34-cd2e-52788ceec919@intel.com>
Date:   Tue, 10 Apr 2018 08:27:48 -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 8:22 AM, Jiri Pirko wrote:
> Tue, Apr 10, 2018 at 05:13:40PM CEST, sridhar.samudrala@...el.com wrote:
>> 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
> Could you also mark the original netdev which is there now? is it
> bypass_netdev or virtio_net_netdev ?

  bypass_netdev
      /     \
     /       \
VF_slave   virtio_net netdev (original)