netdev - [PATCH net-next] xsk: Bring back busy polling support in XDP

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Message-ID: <20250325044358.2675384-1-skhawaja@google.com>
Date: Tue, 25 Mar 2025 04:43:58 +0000
From: Samiullah Khawaja <skhawaja@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>, "David S . Miller " <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, almasrymina@...gle.com, 
	willemb@...gle.com, jdamato@...tly.com, mkarsten@...terloo.ca
Cc: netdev@...r.kernel.org, skhawaja@...gle.com
Subject: [PATCH net-next] xsk: Bring back busy polling support in XDP_COPY

Commit 5ef44b3cb43b ("xsk: Bring back busy polling support") fixed the
busy polling support in xsk for XDP_ZEROCOPY after it was broken in
commit 86e25f40aa1e ("net: napi: Add napi_config"). The busy polling
support with XDP_COPY remained broken since the napi_id setup in
xsk_rcv_check was removed.

Bring back the setup of napi_id for XDP_COPY so socket level SO_BUSYPOLL
can be used to poll the underlying napi.

Tested using AF_XDP support in virtio-net by running the xsk_rr AF_XDP
benchmarking tool shared here:
https://lore.kernel.org/all/20250320163523.3501305-1-skhawaja@google.com/T/

Enabled socket busy polling using following commands in qemu,

```
sudo ethtool -L eth0 combined 1
sudo ethtool -G eth0 rx 1024
echo 400 | sudo tee /proc/sys/net/core/busy_read
echo 100 | sudo tee /sys/class/net/eth0/napi_defer_hard_irqs
echo 15000   | sudo tee /sys/class/net/eth0/gro_flush_timeout
```

Fixes: 5ef44b3cb43b ("xsk: Bring back busy polling support")
Fixes: 86e25f40aa1e ("net: napi: Add napi_config")
Signed-off-by: Samiullah Khawaja <skhawaja@...gle.com>
---
 net/xdp/xsk.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index e5d104ce7b82..de8bf97b2cb9 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -310,6 +310,18 @@ static bool xsk_is_bound(struct xdp_sock *xs)
 	return false;
 }
 
+static void __xsk_mark_napi_id_once(struct sock *sk, struct net_device *dev, u32 qid)
+{
+	struct netdev_rx_queue *rxq;
+
+	if (qid >= dev->real_num_rx_queues)
+		return;
+
+	rxq = __netif_get_rx_queue(dev, qid);
+	if (rxq->napi)
+		__sk_mark_napi_id_once(sk, rxq->napi->napi_id);
+}
+
 static int xsk_rcv_check(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
 {
 	if (!xsk_is_bound(xs))
@@ -323,6 +335,7 @@ static int xsk_rcv_check(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
 		return -ENOSPC;
 	}
 
+	__xsk_mark_napi_id_once(&xs->sk, xs->dev, xs->queue_id);
 	return 0;
 }
 
@@ -1300,13 +1313,8 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
 	xs->queue_id = qid;
 	xp_add_xsk(xs->pool, xs);
 
-	if (xs->zc && qid < dev->real_num_rx_queues) {
-		struct netdev_rx_queue *rxq;
-
-		rxq = __netif_get_rx_queue(dev, qid);
-		if (rxq->napi)
-			__sk_mark_napi_id_once(sk, rxq->napi->napi_id);
-	}
+	if (xs->zc)
+		__xsk_mark_napi_id_once(sk, dev, qid);
 
 out_unlock:
 	if (err) {
-- 
2.49.0.395.g12beb8f557-goog