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: <82f741a2-2512-39de-84c6-874f126c27ea@intel.com>
Date:   Tue, 10 Apr 2018 08:59:02 -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 8:43 AM, Jiri Pirko wrote:
> Tue, Apr 10, 2018 at 05:27:48PM CEST, sridhar.samudrala@...el.com wrote:
>> 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)
> That does not make sense.
> 1) You diverge from the behaviour of the netvsc, where the original
>     netdev is a master of the VF
> 2) If the original netdev is a slave, you cannot have any IP address
>     configured on it (well you could, but the rx_handler would eat every
>     incoming packet). So you will break the user bacause he would have to
>     move the configuration to the new master device.
> This only makes sense that the original netdev becomes the master for both
> netvsc and virtio_net.
Forgot to mention that bypass_netdev takes over the name of the original 
netdev and
virtio_net netdev will get the backup name.
So the userspace network configuration doesn't need to change.