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

[Jiri Pirko <jiri@resnulli.us>]

Wed, Apr 11, 2018 at 04:45:07PM CEST, mst@redhat.com wrote:
>On Wed, Apr 11, 2018 at 10:03:32AM +0200, Jiri Pirko wrote:
>> Wed, Apr 11, 2018 at 08:24:43AM CEST, sridhar.samudrala@intel.com wrote:
>> >On 4/10/2018 11:03 PM, Jiri Pirko wrote:
>> >> Tue, Apr 10, 2018 at 05:59:02PM CEST, sridhar.samudrala@intel.com wrote:
>> >> > On 4/10/2018 8:43 AM, Jiri Pirko wrote:
>> >> > > Tue, Apr 10, 2018 at 05:27:48PM CEST, sridhar.samudrala@intel.com wrote:
>> >> > > > On 4/10/2018 8:22 AM, Jiri Pirko wrote:
>> >> > > > > Tue, Apr 10, 2018 at 05:13:40PM CEST, sridhar.samudrala@intel.com wrote:
>> >> > > > > > On 4/10/2018 3:55 AM, Jiri Pirko wrote:
>> >> > > > > > > Mon, Apr 09, 2018 at 08:47:06PM CEST, sridhar.samudrala@intel.com wrote:
>> >> > > > > > > > On 4/9/2018 1:07 AM, Jiri Pirko wrote:
>> >> > > > > > > > > Sat, Apr 07, 2018 at 12:59:14AM CEST, sridhar.samudrala@intel.com wrote:
>> >> > > > > > > > > > On 4/6/2018 5:48 AM, Jiri Pirko wrote:
>> >> > > > > > > > > > > Thu, Apr 05, 2018 at 11:08:22PM CEST, sridhar.samudrala@intel.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.
>
>If you believe that, then this patchset is a step in the right
>direction.
>
>With something like this patchset applied, converting netvsc to a 3
>device model will presumably be just a flag flip away. Afterwards

If done properly. Yes.

>we'll be able to drop dead code handling the bypass_master flag.
>
>> 
>> >
>> >
>> >> 
>> >> > So the userspace network configuration doesn't need to change.
>> >> > 
>> >> > 
>> >