xsk: avoid double checking against rx queue being full

Currently non-zc xsk rx path for multi-buffer case checks twice if xsk
rx queue has enough space for producing descriptors:
1.
	if (xskq_prod_nb_free(xs->rx, num_desc) < num_desc) {
		xs->rx_queue_full++;
		return -ENOBUFS;
	}
2.
	__xsk_rcv_zc(xs, xskb, copied - meta_len, rem ? XDP_PKT_CONTD : 0);
	-> err = xskq_prod_reserve_desc(xs->rx, addr, len, flags);
	  -> if (xskq_prod_is_full(q))

Second part is redundant as in 1. we already peeked onto rx queue and
checked that there is enough space to produce given amount of
descriptors.

Provide helper functions that will skip it and therefore optimize code.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>

Author: mfijalko

net/xdp/xsk.c

@@ -160,6 +160,17 @@ static int __xsk_rcv_zc(struct xdp_sock *xs, struct xdp_buff_xsk *xskb, u32 len,
 	return 0;
 }
 
+static void __xsk_rcv_zc_safe(struct xdp_sock *xs, struct xdp_buff_xsk *xskb,
+			      u32 len, u32 flags)
+{
+	u64 addr;
+
+	addr = xp_get_handle(xskb, xskb->pool);
+	__xskq_prod_reserve_desc(xs->rx, addr, len, flags);
+
+	xp_release(xskb);
+}
+
 static int xsk_rcv_zc(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
 {
 	struct xdp_buff_xsk *xskb = container_of(xdp, struct xdp_buff_xsk, xdp);
@@ -292,7 +303,8 @@ static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
 		rem -= copied;
 
 		xskb = container_of(xsk_xdp, struct xdp_buff_xsk, xdp);
-		__xsk_rcv_zc(xs, xskb, copied - meta_len, rem ? XDP_PKT_CONTD : 0);
+		__xsk_rcv_zc_safe(xs, xskb, copied - meta_len,
+				  rem ? XDP_PKT_CONTD : 0);
 		meta_len = 0;
 	} while (rem);
 

net/xdp/xsk_queue.h

@@ -445,20 +445,26 @@ static inline void xskq_prod_write_addr_batch(struct xsk_queue *q, struct xdp_de
 	q->cached_prod = cached_prod;
 }
 
-static inline int xskq_prod_reserve_desc(struct xsk_queue *q,
-					 u64 addr, u32 len, u32 flags)
+static inline void __xskq_prod_reserve_desc(struct xsk_queue *q,
+					    u64 addr, u32 len, u32 flags)
 {
 	struct xdp_rxtx_ring *ring = (struct xdp_rxtx_ring *)q->ring;
 	u32 idx;
 
-	if (xskq_prod_is_full(q))
-		return -ENOBUFS;
-
 	/* A, matches D */
 	idx = q->cached_prod++ & q->ring_mask;
 	ring->desc[idx].addr = addr;
 	ring->desc[idx].len = len;
 	ring->desc[idx].options = flags;
+}
+
+static inline int xskq_prod_reserve_desc(struct xsk_queue *q,
+					 u64 addr, u32 len, u32 flags)
+{
+	if (xskq_prod_is_full(q))
+		return -ENOBUFS;
+
+	__xskq_prod_reserve_desc(q, addr, len, flags);
 
 	return 0;
 }