Subject: [PATCH v3] af_xdp kick_tx() Retries instead of endless loop

Subject: [PATCH v3] af_xdp kick_tx() Retries instead of endless loop

[Yan Yanovsky]

From 191d90eaab50c6855ee746361e7e735572f3b1ce Mon Sep 17 00:00:00 2001
From: Yan Yanovsky <yan.yanovsky@catonetworks.com>
Date: Sun, 7 Dec 2025 18:10:45 +0200
Subject: [PATCH v3] af_xdp kick_tx() Retries instead of endless loop
 Signed-off-by: Yan Yanovsky <yan.yanovsky@catonetworks.com>

---
 drivers/net/af_xdp/rte_eth_af_xdp.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c b/drivers/net/af_xdp/rte_eth_af_xdp.c
index b6ec9bf490..dc34f1a29e 100644
--- a/drivers/net/af_xdp/rte_eth_af_xdp.c
+++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
@@ -80,6 +80,7 @@ RTE_LOG_REGISTER_DEFAULT(af_xdp_logtype, NOTICE);
 #define ETH_AF_XDP_ETH_OVERHEAD		(RTE_ETHER_HDR_LEN + RTE_ETHER_CRC_LEN)
 
 #define ETH_AF_XDP_MP_KEY "afxdp_mp_send_fds"
+#define MAX_TX_KICK_TRIES	10
 
 static int afxdp_dev_count;
 
@@ -480,22 +481,29 @@ static void
 kick_tx(struct pkt_tx_queue *txq, struct xsk_ring_cons *cq)
 {
 	struct xsk_umem_info *umem = txq->umem;
+	int tries = 0;
 
+	/* Pull completion queue entries to free UMEM buffers */
 	pull_umem_cq(umem, XSK_RING_CONS__DEFAULT_NUM_DESCS, cq);
 
-	if (tx_syscall_needed(&txq->tx))
-		while (send(xsk_socket__fd(txq->pair->xsk), NULL,
-			    0, MSG_DONTWAIT) < 0) {
-			/* some thing unexpected */
-			if (errno != EBUSY && errno != EAGAIN && errno != EINTR)
-				break;
+	if (!tx_syscall_needed(&txq->tx))
+		return;
 
-			/* pull from completion queue to leave more space */
-			if (errno == EAGAIN)
+	for (tries = 0; tries < MAX_TX_KICK_TRIES; tries++) {
+		if (send(xsk_socket__fd(txq->pair->xsk), NULL, 0,
+				MSG_DONTWAIT) >= 0)
+			break;
+		if (errno != EBUSY && errno != EAGAIN && errno != EINTR)
+			break;
+
+		if (errno == EAGAIN) {
+			/* Kernel TX ring has no space or UMEM completion queue
+			*  is lagging behind. Try pulling CQ to free room. */\
 				pull_umem_cq(umem,
-					     XSK_RING_CONS__DEFAULT_NUM_DESCS,
-					     cq);
+						XSK_RING_CONS__DEFAULT_NUM_DESCS, 
+						cq);
 		}
+	}
 }
 
 #if defined(XDP_UMEM_UNALIGNED_CHUNK_FLAG)
-- 
2.39.5

Re: Subject: [PATCH v3] af_xdp kick_tx() Retries instead of endless loop

[Stephen Hemminger]

On Mon, 8 Dec 2025 15:56:37 +0000
Yan Yanovsky <yan.yanovsky@catonetworks.com> wrote:

> From 191d90eaab50c6855ee746361e7e735572f3b1ce Mon Sep 17 00:00:00 2001
> From: Yan Yanovsky <yan.yanovsky@catonetworks.com>
> Date: Sun, 7 Dec 2025 18:10:45 +0200
> Subject: [PATCH v3] af_xdp kick_tx() Retries instead of endless loop
>  Signed-off-by: Yan Yanovsky <yan.yanovsky@catonetworks.com>
> 

Minor cosmetic changes needed.

>  drivers/net/af_xdp/rte_eth_af_xdp.c | 28 ++++++++++++++++++----------
>  1 file changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c b/drivers/net/af_xdp/rte_eth_af_xdp.c
> index b6ec9bf490..dc34f1a29e 100644
> --- a/drivers/net/af_xdp/rte_eth_af_xdp.c
> +++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
> @@ -80,6 +80,7 @@ RTE_LOG_REGISTER_DEFAULT(af_xdp_logtype, NOTICE);
>  #define ETH_AF_XDP_ETH_OVERHEAD		(RTE_ETHER_HDR_LEN + RTE_ETHER_CRC_LEN)
>  
>  #define ETH_AF_XDP_MP_KEY "afxdp_mp_send_fds"
> +#define MAX_TX_KICK_TRIES	10
>  
>  static int afxdp_dev_count;
>  
> @@ -480,22 +481,29 @@ static void
>  kick_tx(struct pkt_tx_queue *txq, struct xsk_ring_cons *cq)
>  {
>  	struct xsk_umem_info *umem = txq->umem;
> +	int tries = 0;
>  

Unnecessary initialization

> +	/* Pull completion queue entries to free UMEM buffers */
>  	pull_umem_cq(umem, XSK_RING_CONS__DEFAULT_NUM_DESCS, cq);
>  
> -	if (tx_syscall_needed(&txq->tx))
> -		while (send(xsk_socket__fd(txq->pair->xsk), NULL,
> -			    0, MSG_DONTWAIT) < 0) {
> -			/* some thing unexpected */
> -			if (errno != EBUSY && errno != EAGAIN && errno != EINTR)
> -				break;
> +	if (!tx_syscall_needed(&txq->tx))
> +		return;
>  
> -			/* pull from completion queue to leave more space */
> -			if (errno == EAGAIN)
> +	for (tries = 0; tries < MAX_TX_KICK_TRIES; tries++) {

Suggest (but not required) to put definition here as:
	for (unsigned int tries = 0; tries < MAX_TX_KICK_TRIES; tries++) {

> +		if (send(xsk_socket__fd(txq->pair->xsk), NULL, 0,
> +				MSG_DONTWAIT) >= 0)
> +			break;
> +		if (errno != EBUSY && errno != EAGAIN && errno != EINTR)
> +			break;
> +
> +		if (errno == EAGAIN) {
> +			/* Kernel TX ring has no space or UMEM completion queue
> +			*  is lagging behind. Try pulling CQ to free room. */\
>  				pull_umem_cq(umem,

Do not put line continuation on the comment.
Original indent is better. I.e line up args on first to same column

> -					     XSK_RING_CONS__DEFAULT_NUM_DESCS,
> -					     cq);
> +						XSK_RING_CONS__DEFAULT_NUM_DESCS, 
> +						cq);
>  		}
> +	}
>  }
>  
>  #if defined(XDP_UMEM_UNALIGNED_CHUNK_FLAG)

Subject is repeated twice.