Re: [virtio-dev] Re: [PATCH v7 net-next 2/4] net: Introduce generic failover module

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Apr 20, 2018 at 08:56:57AM -0700, Alexander Duyck wrote:
> On Fri, Apr 20, 2018 at 8:34 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Fri, Apr 20, 2018 at 08:21:00AM -0700, Samudrala, Sridhar wrote:
> >> > > + finfo = netdev_priv(failover_dev);
> >> > > +
> >> > > + primary_dev = rtnl_dereference(finfo->primary_dev);
> >> > > + standby_dev = rtnl_dereference(finfo->standby_dev);
> >> > > +
> >> > > + if (slave_dev != primary_dev && slave_dev != standby_dev)
> >> > > +         goto done;
> >> > > +
> >> > > + if ((primary_dev && failover_xmit_ready(primary_dev)) ||
> >> > > +     (standby_dev && failover_xmit_ready(standby_dev))) {
> >> > > +         netif_carrier_on(failover_dev);
> >> > > +         netif_tx_wake_all_queues(failover_dev);
> >> > > + } else {
> >> > > +         netif_carrier_off(failover_dev);
> >> > > +         netif_tx_stop_all_queues(failover_dev);
> >> > And I think it's a good idea to get stats from device here too.
> >>
> >> Not sure why we need to get stats from lower devs here?
> >
> > link down is often indication of a hardware problem.
> > lower dev might stop responding down the road.
> >
> >> > > +static const struct net_device_ops failover_dev_ops = {
> >> > > + .ndo_open               = failover_open,
> >> > > + .ndo_stop               = failover_close,
> >> > > + .ndo_start_xmit         = failover_start_xmit,
> >> > > + .ndo_select_queue       = failover_select_queue,
> >> > > + .ndo_get_stats64        = failover_get_stats,
> >> > > + .ndo_change_mtu         = failover_change_mtu,
> >> > > + .ndo_set_rx_mode        = failover_set_rx_mode,
> >> > > + .ndo_validate_addr      = eth_validate_addr,
> >> > > + .ndo_features_check     = passthru_features_check,
> >> > xdp support?
> >>
> >> I think it should be possible to add it be calling the lower dev ndo_xdp routines
> >> with proper checks. can we add this later?
> >
> > I'd be concerned that if you don't xdp userspace will keep poking
> > at lower devs. Then it will stop working if you add this later.
> 
> The failover device is better off not providing in-driver XDP since
> there are already skbs allocated by the time that we see the packet
> here anyway. As such generic XDP is the preferred way to handle this
> since it will work regardless of what lower devices are present.
>
> The only advantage of having XDP down at the virtio or VF level would
> be that it performs better, but at the cost of complexity since we
> would need to rebind the eBPF program any time a device is hotplugged
> out and then back in. For now the current approach is in keeping with
> how bonding and other similar drivers are currently handling this.
> 
> Thanks.
> 
> - Alex

OK fair enough.

-- 
MST

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