Re: [PATCH 4/5] virtio_net: add dedicated XDP transmit queues

[Jakub Kicinski]

On Fri, 18 Nov 2016 13:09:53 -0800, Jakub Kicinski wrote:
> Looks very cool! :)
> 
> On Fri, 18 Nov 2016 11:00:41 -0800, John Fastabend wrote:
> > @@ -1542,12 +1546,34 @@ static int virtnet_xdp_set(struct net_device *dev, 
> > struct bpf_prog *prog)
> >             return -EINVAL;
> >     }
> >  
> > +   curr_qp = vi->curr_queue_pairs - vi->xdp_queue_pairs;
> > +   if (prog)
> > +           xdp_qp = num_online_cpus();  
> 
> Is num_online_cpus() correct here?

Sorry, I don't know the virto_net code, so I'm probably wrong.  I was
concerned whether the number of cpus can change but also that the cpu
mask may be sparse and therefore offsetting by smp_processor_id()
into the queue table below could bring trouble.

@@ -353,9 +381,15 @@ static u32 do_xdp_prog(struct virtnet_info *vi,
        switch (act) {
        case XDP_PASS:
                return XDP_PASS;
+       case XDP_TX:
+               qp = vi->curr_queue_pairs -
+                       vi->xdp_queue_pairs +
+                       smp_processor_id();
+               xdp.data = buf + (vi->mergeable_rx_bufs ? 0 : 4);
+               virtnet_xdp_xmit(vi, qp, &xdp);
+               return XDP_TX;
        default:
                bpf_warn_invalid_xdp_action(act);
-       case XDP_TX:
        case XDP_ABORTED:
        case XDP_DROP:
                return XDP_DROP;