On Mon, Sep 12, 2016 at 03:46:39PM -0700, Eric Dumazet wrote:
> On Mon, 2016-09-12 at 15:13 -0700, John Fastabend wrote:
> > From: Alexei Starovoitov <a...@fb.com>
>
> > +static void e1000_xmit_raw_frame(struct e1000_rx_buffer *rx_buffer_info,
> > + u32 len,
> > + struct net_device *netdev,
> > + struct e1000_adapter *adapter)
> > +{
> > + struct netdev_queue *txq = netdev_get_tx_queue(netdev, 0);
> > + struct e1000_hw *hw = &adapter->hw;
> > + struct e1000_tx_ring *tx_ring;
> > +
> > + if (len > E1000_MAX_DATA_PER_TXD)
> > + return;
> > +
> > + /* e1000 only support a single txq at the moment so the queue is being
> > + * shared with stack. To support this requires locking to ensure the
> > + * stack and XDP are not running at the same time. Devices with
> > + * multiple queues should allocate a separate queue space.
> > + */
> > + HARD_TX_LOCK(netdev, txq, smp_processor_id());
> > +
> > + tx_ring = adapter->tx_ring;
> > +
> > + if (E1000_DESC_UNUSED(tx_ring) < 2) {
> > + HARD_TX_UNLOCK(netdev, txq);
> > + return;
> > + }
> > +
> > + if (netif_xmit_frozen_or_stopped(txq))
> > + return;
> > +
> > + e1000_tx_map_rxpage(tx_ring, rx_buffer_info, len);
> > + netdev_sent_queue(netdev, len);
> > + e1000_tx_queue(adapter, tx_ring, 0/*tx_flags*/, 1);
> > +
> > + writel(tx_ring->next_to_use, hw->hw_addr + tx_ring->tdt);
> > + mmiowb();
> > +
> > + HARD_TX_UNLOCK(netdev, txq);
> > +}
>
>
> e1000_tx_map() is full of workarounds.
>
> Have a look at last_tx_tso for example.
>
> /* Workaround for Controller erratum --
> * descriptor for non-tso packet in a linear SKB that follows
> a
> * tso gets written back prematurely before the data is fully
> * DMA'd to the controller
> */
> if (!skb->data_len && tx_ring->last_tx_tso &&
> !skb_is_gso(skb)) {
> tx_ring->last_tx_tso = false;
> size -= 4;
> }
>
> Look, this XDP_TX thing is hard to properly implement and test on
> various NIC revisions.
my reading of these e1k workarounds are for old versions of the nic that
don't even exist anymore. I believe none of them apply to qemu e1k.
> Without proper queue management, high prio packets in qdisc wont be sent
> if NIC is under RX -> XDP_TX flood.
yep. there are various ways to shoot yourself in the foot with xdp.
The simplest program that drops all the packets will make the box unpingable.
> Sounds a horrible feature to me.
yep. not pretty by any means.
This whole thing is only to test xdp programs under qemu which
realistically emulates only e1k.
I simply don't see any other options to test xdp under kvm.
