netdev - [PATCH net-next] net: xsk: update tx queue consumer immdiately after transmission

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Message-Id: <20250619093641.70700-1-kerneljasonxing@gmail.com>
Date: Thu, 19 Jun 2025 17:36:41 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	bjorn@...nel.org,
	magnus.karlsson@...el.com,
	maciej.fijalkowski@...el.com,
	jonathan.lemon@...il.com,
	sdf@...ichev.me,
	ast@...nel.org,
	daniel@...earbox.net,
	hawk@...nel.org,
	john.fastabend@...il.com,
	joe@...a.to,
	willemdebruijn.kernel@...il.com
Cc: bpf@...r.kernel.org,
	netdev@...r.kernel.org,
	Jason Xing <kernelxing@...cent.com>
Subject: [PATCH net-next] net: xsk: update tx queue consumer immdiately after transmission

From: Jason Xing <kernelxing@...cent.com>

For afxdp, the return value of sendto() syscall doesn't reflect how many
descs handled in the kernel. One of use cases is that when user-space
application tries to know the number of transmitted skbs and then decides
if it continues to send, say, is it stopped due to max tx budget?

The following formular can be used after sending to learn how many
skbs/descs the kernel takes care of:

  tx_queue.consumers_before - tx_queue.consumers_after

Prior to the current patch, the consumer of tx queue is not immdiately
updated at the end of each sendto syscall, which leads the consumer
value out-of-dated from the perspective of user space. So this patch
requires store operation to pass the cached value to the shared value
to handle the problem.

Signed-off-by: Jason Xing <kernelxing@...cent.com>
---
 net/xdp/xsk.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 7c47f665e9d1..3288ab2d67b4 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -856,6 +856,8 @@ static int __xsk_generic_xmit(struct sock *sk)
 	}

 out:
+	__xskq_cons_release(xs->tx);
+
 	if (sent_frame)
 		if (xsk_tx_writeable(xs))
 			sk->sk_write_space(sk);
-- 
2.43.5