On Mon, 2016-09-12 at 09:21 -0700, Tom Herbert wrote:
> In order to use XDP with non multi-queue drivers (such as e1000) we need
> a method to handle XDP_TX return code from xdp program. Since there is
> only one queue the XDP transmit path needs to share that queue with the
> normal stack path, and in order to do that we can't break the existing
> stack's mechanisms of locking, qdiscs, and BQL for the queue.
>
> This patch allocates an skbuff when XDP_TX is returned from the XDP
> program and call dev_queue_xmit to transmit the skbuff.
>
> Note that this is expected to be a performance hit (which needs to be
> quantified) relative to a MQ XDP implementation where we can reserve
> queues to be used by XDP. The first intent of these patches is
> correctness. This should not affect performance in the XDP_DROP path.
>
> This patch needs to be applied after "e1000: add initial XDP support".
>
> Tested: I've only built this, need to see if I can find some e1000
> machines. John, if you could try this that would be much appreciated.
>
> Signed-off-by: Tom Herbert <t...@herbertland.com>
> ---
> drivers/net/ethernet/intel/e1000/e1000_main.c | 29
> ++++++++++++++++++++-------
> 1 file changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c
> b/drivers/net/ethernet/intel/e1000/e1000_main.c
> index 91d5c87..f457ea8 100644
> --- a/drivers/net/ethernet/intel/e1000/e1000_main.c
> +++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
> @@ -4338,13 +4338,28 @@ static bool e1000_clean_jumbo_rx_irq(struct
> e1000_adapter *adapter,
> case XDP_PASS:
> break;
> case XDP_TX:
> - dma_sync_single_for_device(&pdev->dev,
> - dma,
> - length,
> - DMA_TO_DEVICE);
> - e1000_xmit_raw_frame(buffer_info, length,
> - netdev, adapter);
> - buffer_info->rxbuf.page = NULL;
> + /* There is only one transmit queue so we need
> + * to inject the packet at the qdisc layer
> + * to maintain sanity in the stack. We allocate
> + * an skbuff, set up frags with the page, and
> + * then do dev_queue_xmit.
> + */
> + skb = alloc_skb(0, GFP_ATOMIC);
> + if (skb) {
> + dma_unmap_page(&pdev->dev,
> + buffer_info->dma,
> + adapter->rx_buffer_len,
> + DMA_FROM_DEVICE);
> + skb->dev = netdev;
> + skb_fill_page_desc(skb, 0,
> + buffer_info->rxbuf.page,
> + 0, length);
> + dev_queue_xmit(skb);
> + goto next_desc;
> + }
> + /* Fallthrough, if we are unable to handle
> + * XDP_TX then we need to drop.
> + */
> case XDP_DROP:
> default:
> /* re-use mapped page. keep buffer_info->dma
If the intent is correctness, then you'll need to populate skb->len and
skb->data_len.
Also many drivers assume some headers are in skb->head.
e1000 seems to assume skb_headlen() can not be 0
