netdev - [PATCH net-next 1/2] xsk: avoid using heavy lock when the pool is not shared

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Message-Id: <20251025065310.5676-2-kerneljasonxing@gmail.com>
Date: Sat, 25 Oct 2025 14:53:09 +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,
	horms@...nel.org,
	andrew+netdev@...n.ch
Cc: bpf@...r.kernel.org,
	netdev@...r.kernel.org,
	Jason Xing <kernelxing@...cent.com>
Subject: [PATCH net-next 1/2] xsk: avoid using heavy lock when the pool is not shared

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

The commit f09ced4053bc ("xsk: Fix race in SKB mode transmit with
shared cq") uses a heavy lock (spin_lock_irqsave) for the shared
pool scenario which is that multiple sockets share the same pool.

It does harm to the case where the pool is only owned by one xsk.
The patch distinguishes those two cases through checking if the xsk
list only has one xsk. If so, that means the pool is exclusive and
we don't need to hold the lock and disable IRQ at all. The benefit
of this is to avoid those two operations being executed extremely
frequently.

With this patch, the performance number[1] could go from 1,872,565 pps
to 2,147,803 pps. It's a noticeable rise of around 14.6%.

[1]: taskset -c 1 ./xdpsock -i enp2s0f1 -q 0 -t -S -s 64

Signed-off-by: Jason Xing <kernelxing@...cent.com>
---
 net/xdp/xsk.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 7b0c68a70888..76f797fcc49c 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -548,12 +548,15 @@ static int xsk_wakeup(struct xdp_sock *xs, u8 flags)
 
 static int xsk_cq_reserve_locked(struct xsk_buff_pool *pool)
 {
+	bool lock = !list_is_singular(&pool->xsk_tx_list);
 	unsigned long flags;
 	int ret;
 
-	spin_lock_irqsave(&pool->cq_lock, flags);
+	if (lock)
+		spin_lock_irqsave(&pool->cq_lock, flags);
 	ret = xskq_prod_reserve(pool->cq);
-	spin_unlock_irqrestore(&pool->cq_lock, flags);
+	if (lock)
+		spin_unlock_irqrestore(&pool->cq_lock, flags);
 
 	return ret;
 }
@@ -588,11 +591,14 @@ static void xsk_cq_submit_addr_locked(struct xsk_buff_pool *pool,
 
 static void xsk_cq_cancel_locked(struct xsk_buff_pool *pool, u32 n)
 {
+	bool lock = !list_is_singular(&pool->xsk_tx_list);
 	unsigned long flags;
 
-	spin_lock_irqsave(&pool->cq_lock, flags);
+	if (lock)
+		spin_lock_irqsave(&pool->cq_lock, flags);
 	xskq_prod_cancel_n(pool->cq, n);
-	spin_unlock_irqrestore(&pool->cq_lock, flags);
+	if (lock)
+		spin_unlock_irqrestore(&pool->cq_lock, flags);
 }
 
 static void xsk_inc_num_desc(struct sk_buff *skb)
-- 
2.41.3