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

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Date:   Wed, 11 Apr 2018 10:03:32 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
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

Wed, Apr 11, 2018 at 08:24:43AM CEST, sridhar.samudrala@...el.com wrote:
>On 4/10/2018 11:03 PM, Jiri Pirko wrote:
>> Tue, Apr 10, 2018 at 05:59:02PM CEST, sridhar.samudrala@...el.com wrote:
>> > 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.
>> What do you mean by "name"?
>
>bypass_netdev also is associated with the same pci device as the original virtio_net
>netdev via SET_NETDEV_DEV().  Also, we added ndo_get_phys_port_name() to virtio_net
>that will return _bkup when BACKUP feature is enabled.

Okay.

>
>So for ex: if virtio_net inteface was getting 'ens12' as the name assigned by udev
>without BACKUP feature,  when BACKUP feature is enabled,  the  bypass_netdev will be
>named 'ens12' and the original virtio_net will get named as ens12n_bkup.

Got it.

I don't like the bypass_master to look differently in netvsc and
virtio_net :/ The best would be to convert netvsc to 3 netdev model and
treat them the same. The more I think about it, the more the 2 netdev
model feels wrong.


>
>
>> 
>> > So the userspace network configuration doesn't need to change.
>> > 
>> > 
>