xsk: Change the tx writeable condition

Modify the tx writeable condition from the queue is not full to the number of present tx queues is less than the half of the total number of queues. Because the tx queue not full is a very short time, this will cause a large number of EPOLLOUT events, and cause a large number of process wake up. Fixes: 35fcde7 ("xsk: support for Tx") Signed-off-by: Xuan Zhuo <[email protected]> Signed-off-by: Daniel Borkmann <[email protected]> Acked-by: Magnus Karlsson <[email protected]> Link: https://lore.kernel.org/bpf/508fef55188d4e1160747ead64c6dcda36735880.1606555939.git.xuanzhuo@linux.alibaba.com
chewitt · Dec 3, 2020 · 3413f04 · 3413f04
1 parent f5da541
commit 3413f04
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Showing 2 changed files with 19 additions and 3 deletions.
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
@@ -211,6 +211,14 @@ static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len,
 	return 0;
 }
 
+static bool xsk_tx_writeable(struct xdp_sock *xs)
+{
+	if (xskq_cons_present_entries(xs->tx) > xs->tx->nentries / 2)
+		return false;
+
+	return true;
+}
+
 static bool xsk_is_bound(struct xdp_sock *xs)
 {
 	if (READ_ONCE(xs->state) == XSK_BOUND) {
@@ -296,7 +304,8 @@ void xsk_tx_release(struct xsk_buff_pool *pool)
 	rcu_read_lock();
 	list_for_each_entry_rcu(xs, &pool->xsk_tx_list, tx_list) {
 		__xskq_cons_release(xs->tx);
-		xs->sk.sk_write_space(&xs->sk);
+		if (xsk_tx_writeable(xs))
+			xs->sk.sk_write_space(&xs->sk);
 	}
 	rcu_read_unlock();
 }
@@ -436,7 +445,8 @@ static int xsk_generic_xmit(struct sock *sk)
 
 out:
 	if (sent_frame)
-		sk->sk_write_space(sk);
+		if (xsk_tx_writeable(xs))
+			sk->sk_write_space(sk);
 
 	mutex_unlock(&xs->mutex);
 	return err;
@@ -493,7 +503,7 @@ static __poll_t xsk_poll(struct file *file, struct socket *sock,
 
 	if (xs->rx && !xskq_prod_is_empty(xs->rx))
 		mask |= EPOLLIN | EPOLLRDNORM;
-	if (xs->tx && !xskq_cons_is_full(xs->tx))
+	if (xs->tx && xsk_tx_writeable(xs))
 		mask |= EPOLLOUT | EPOLLWRNORM;
 
 	return mask;

diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
@@ -264,6 +264,12 @@ static inline bool xskq_cons_is_full(struct xsk_queue *q)
 		q->nentries;
 }
 
+static inline u32 xskq_cons_present_entries(struct xsk_queue *q)
+{
+	/* No barriers needed since data is not accessed */
+	return READ_ONCE(q->ring->producer) - READ_ONCE(q->ring->consumer);
+}
+
 /* Functions for producers */
 
 static inline bool xskq_prod_is_full(struct xsk_queue *q)