On Mon, 2016-09-12 at 15:13 -0700, John Fastabend wrote:
> From: Alexei Starovoitov <[email protected]>
> +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.
Without proper queue management, high prio packets in qdisc wont be sent
if NIC is under RX -> XDP_TX flood.
Sounds a horrible feature to me.
