xsk: Add API to check for available entries in FQ

Add a function that checks whether the Fill Ring has the specified
amount of descriptors available. It will be useful for mlx5e that wants
to check in advance, whether it can allocate a bulk of RX descriptors,
to get the best performance.

Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/net/xdp_sock.h

@@ -77,6 +77,7 @@ int xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);
 void xsk_flush(struct xdp_sock *xs);
 bool xsk_is_setup_for_bpf_map(struct xdp_sock *xs);
 /* Used from netdev driver */
+bool xsk_umem_has_addrs(struct xdp_umem *umem, u32 cnt);
 u64 *xsk_umem_peek_addr(struct xdp_umem *umem, u64 *addr);
 void xsk_umem_discard_addr(struct xdp_umem *umem);
 void xsk_umem_complete_tx(struct xdp_umem *umem, u32 nb_entries);
@@ -99,6 +100,16 @@ static inline dma_addr_t xdp_umem_get_dma(struct xdp_umem *umem, u64 addr)
 }
 
 /* Reuse-queue aware version of FILL queue helpers */
+static inline bool xsk_umem_has_addrs_rq(struct xdp_umem *umem, u32 cnt)
+{
+	struct xdp_umem_fq_reuse *rq = umem->fq_reuse;
+
+	if (rq->length >= cnt)
+		return true;
+
+	return xsk_umem_has_addrs(umem, cnt - rq->length);
+}
+
 static inline u64 *xsk_umem_peek_addr_rq(struct xdp_umem *umem, u64 *addr)
 {
 	struct xdp_umem_fq_reuse *rq = umem->fq_reuse;
@@ -146,6 +157,11 @@ static inline bool xsk_is_setup_for_bpf_map(struct xdp_sock *xs)
 	return false;
 }
 
+static inline bool xsk_umem_has_addrs(struct xdp_umem *umem, u32 cnt)
+{
+	return false;
+}
+
 static inline u64 *xsk_umem_peek_addr(struct xdp_umem *umem, u64 *addr)
 {
 	return NULL;
@@ -200,6 +216,11 @@ static inline dma_addr_t xdp_umem_get_dma(struct xdp_umem *umem, u64 addr)
 	return 0;
 }
 
+static inline bool xsk_umem_has_addrs_rq(struct xdp_umem *umem, u32 cnt)
+{
+	return false;
+}
+
 static inline u64 *xsk_umem_peek_addr_rq(struct xdp_umem *umem, u64 *addr)
 {
 	return NULL;

net/xdp/xsk.c

@@ -37,6 +37,12 @@ bool xsk_is_setup_for_bpf_map(struct xdp_sock *xs)
 		READ_ONCE(xs->umem->fq);
 }
 
+bool xsk_umem_has_addrs(struct xdp_umem *umem, u32 cnt)
+{
+	return xskq_has_addrs(umem->fq, cnt);
+}
+EXPORT_SYMBOL(xsk_umem_has_addrs);
+
 u64 *xsk_umem_peek_addr(struct xdp_umem *umem, u64 *addr)
 {
 	return xskq_peek_addr(umem->fq, addr);

net/xdp/xsk_queue.h

@@ -117,6 +117,20 @@ static inline u32 xskq_nb_free(struct xsk_queue *q, u32 producer, u32 dcnt)
 	return q->nentries - (producer - q->cons_tail);
 }
 
+static inline bool xskq_has_addrs(struct xsk_queue *q, u32 cnt)
+{
+	u32 entries = q->prod_tail - q->cons_tail;
+
+	if (entries >= cnt)
+		return true;
+
+	/* Refresh the local pointer. */
+	q->prod_tail = READ_ONCE(q->ring->producer);
+	entries = q->prod_tail - q->cons_tail;
+
+	return entries >= cnt;
+}
+
 /* UMEM queue */
 
 static inline bool xskq_is_valid_addr(struct xsk_queue *q, u64 addr)