netdev - [PATCH net v2] xsk: Bring back busy polling support in XDP

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Message-ID: <20250516213638.1889546-1-skhawaja@google.com>
Date: Fri, 16 May 2025 21:36:38 +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, stfomichev@...il.com
Cc: netdev@...r.kernel.org, skhawaja@...gle.com
Subject: [PATCH net v2] 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.

Do the setup of napi_id for XDP_COPY in xsk_bind, as it is done
currently for XDP_ZEROCOPY. The setup of napi_id for XDP_COPY in
xsk_bind is safe because xsk_rcv_check checks that the rx queue at which
the packet arrives is equal to the queue_id that was supplied in bind.
This is done for both XDP_COPY and XDP_ZEROCOPY mode.

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
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")
Signed-off-by: Samiullah Khawaja <skhawaja@...gle.com>
Reviewed-by: Willem de Bruijn <willemb@...gle.com>
---

v2:
- Mark Napi ID in xsk_bind for XDP_COPY.

v1:
https://lore.kernel.org/netdev/Z-Lby6WMFkHaaJxB@mini-arch/T/#mdd713c1e2b0caf3bb5f625884709af95e30ccc4d

 net/xdp/xsk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 4abc81f33d3e..72c000c0ae5f 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -1304,7 +1304,7 @@ 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) {
+	if (qid < dev->real_num_rx_queues) {
 		struct netdev_rx_queue *rxq;

 		rxq = __netif_get_rx_queue(dev, qid);
-- 
2.49.0.1112.g889b7c5bd8-goog