[E1000-devel] what's the performance of X520 without RSS

[Jon Z. <Jon...@jd...>]

Hi

The reason I want to disable RSS is that I doubt it will incur packet mis-order in af_packet.c/PACKET_MMAP
i.e.
In multi-queue enabled kernel, tpacket_rcv will be run in parallel,right? So that a later packet might get the spinlock earlier and it is copied to the ring buffer prior to packet which timestamp is earlier?
if RSS is disabled the tpacket_rcv will be run in sequence, but what's the performance? Can intel X520 nic reach 5gbps+ without RSS?

Thanks
jon

af_packet.c
static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
                      struct packet_type *pt, struct net_device *orig_dev)
{
...
spin_lock(&sk->sk_receive_queue.lock);
       h.raw = packet_current_frame(po, &po->rx_ring, TP_STATUS_KERNEL);
       if (!h.raw)
               goto ring_is_full;
       packet_increment_head(&po->rx_ring);
       po->stats.tp_packets++;
       if (copy_skb) {
               status |= TP_STATUS_COPY;
               __skb_queue_tail(&sk->sk_receive_queue, copy_skb);
       }
       if (!po->stats.tp_drops)
               status &= ~TP_STATUS_LOSING;
       spin_unlock(&sk->sk_receive_queue.lock);

       skb_copy_bits(skb, 0, h.raw + macoff, snaplen);
}