[v2,1/3] net/af_xdp: fix Tx halt when no recv packets

  From: Xiaolong Ye <xiaolong.ye@intel.com>

The kernel only consumes Tx packets if we have some Rx traffic on specified
queue or we have called send(). So we need to issue a send() even when the
allocation fails so that kernel will start to consume packets again.

Commit 45bba02c95b0 ("net/af_xdp: support need wakeup feature") breaks
above rule by adding some condition to send, this patch fixes it while
still keeps the need_wakeup feature for Tx.

Fixes: 45bba02c95b0 ("net/af_xdp: support need wakeup feature")
Cc: stable@dpdk.org

Signed-off-by: Xiaolong Ye <xiaolong.ye@intel.com>
Tested-by: Ciara Loftus <ciara.loftus@intel.com>
---
 drivers/net/af_xdp/rte_eth_af_xdp.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)
  

Hi, 

As this is indeed a kernel driver issue, and Magnus is working on the workaound/fix
in i40e kernel driver, as long as the workaound/fix can be merged in v5.4, this
patch can be dropped.

Thanks,
Xiaolong

On 09/30, Ciara Loftus wrote:
>From: Xiaolong Ye <xiaolong.ye@intel.com>
>
>The kernel only consumes Tx packets if we have some Rx traffic on specified
>queue or we have called send(). So we need to issue a send() even when the
>allocation fails so that kernel will start to consume packets again.
>
>Commit 45bba02c95b0 ("net/af_xdp: support need wakeup feature") breaks
>above rule by adding some condition to send, this patch fixes it while
>still keeps the need_wakeup feature for Tx.
>
>Fixes: 45bba02c95b0 ("net/af_xdp: support need wakeup feature")
>Cc: stable@dpdk.org
>
>Signed-off-by: Xiaolong Ye <xiaolong.ye@intel.com>
>Tested-by: Ciara Loftus <ciara.loftus@intel.com>
>---
> drivers/net/af_xdp/rte_eth_af_xdp.c | 28 ++++++++++++++--------------
> 1 file changed, 14 insertions(+), 14 deletions(-)
>
>diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c b/drivers/net/af_xdp/rte_eth_af_xdp.c
>index 41ed5b2af..e496e9aaa 100644
>--- a/drivers/net/af_xdp/rte_eth_af_xdp.c
>+++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
>@@ -286,19 +286,16 @@ kick_tx(struct pkt_tx_queue *txq)
> {
> 	struct xsk_umem_info *umem = txq->pair->umem;
> 
>-#if defined(XDP_USE_NEED_WAKEUP)
>-	if (xsk_ring_prod__needs_wakeup(&txq->tx))
>-#endif
>-		while (send(xsk_socket__fd(txq->pair->xsk), NULL,
>-			    0, MSG_DONTWAIT) < 0) {
>-			/* some thing unexpected */
>-			if (errno != EBUSY && errno != EAGAIN && errno != EINTR)
>-				break;
>-
>-			/* pull from completion queue to leave more space */
>-			if (errno == EAGAIN)
>-				pull_umem_cq(umem, ETH_AF_XDP_TX_BATCH_SIZE);
>-		}
>+	while (send(xsk_socket__fd(txq->pair->xsk), NULL,
>+		    0, MSG_DONTWAIT) < 0) {
>+		/* some thing unexpected */
>+		if (errno != EBUSY && errno != EAGAIN && errno != EINTR)
>+			break;
>+
>+		/* pull from completion queue to leave more space */
>+		if (errno == EAGAIN)
>+			pull_umem_cq(umem, ETH_AF_XDP_TX_BATCH_SIZE);
>+	}
> 	pull_umem_cq(umem, ETH_AF_XDP_TX_BATCH_SIZE);
> }
> 
>@@ -367,7 +364,10 @@ eth_af_xdp_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
> 
> 	xsk_ring_prod__submit(&txq->tx, nb_pkts);
> 
>-	kick_tx(txq);
>+#if defined(XDP_USE_NEED_WAKEUP)
>+	if (xsk_ring_prod__needs_wakeup(&txq->tx))
>+#endif
>+		kick_tx(txq);
> 
> 	txq->stats.tx_pkts += nb_pkts;
> 	txq->stats.tx_bytes += tx_bytes;
>-- 
>2.17.1
>