From: Ciara Loftus <ciara.loftus@intel.com>
Date: Tue, 20 Apr 2021 08:44:31 +0000 (+0100)
Subject: net/af_xdp: use recvfrom only if busy polling enabled
X-Git-Url: http://git.droids-corp.org/?p=dpdk.git;a=commitdiff_plain;h=b42cffab059ea525566d54e3daf4ba5fcf0d62e1

net/af_xdp: use recvfrom only if busy polling enabled

The recvfrom() syscall is only supported by AF_XDP sockets since
kernel 5.11. Only use it if busy polling is configured. We can
assume a kernel >= 5.11 is in use if busy polling is configured
so we can safely call recvfrom() in that case.

Fixes: 63e8989fe5a4 ("net/af_xdp: use recvfrom instead of poll syscall")

Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
---

diff --git a/drivers/net/af_xdp/compat.h b/drivers/net/af_xdp/compat.h
index 9de9454885..52fd447b69 100644
--- a/drivers/net/af_xdp/compat.h
+++ b/drivers/net/af_xdp/compat.h
@@ -4,6 +4,7 @@
 
 #include <bpf/xsk.h>
 #include <linux/version.h>
+#include <poll.h>
 
 #if KERNEL_VERSION(5, 10, 0) <= LINUX_VERSION_CODE && \
 	defined(RTE_LIBRTE_AF_XDP_PMD_SHARED_UMEM)
@@ -41,10 +42,22 @@ create_shared_socket(struct xsk_socket **xsk_ptr __rte_unused,
 #endif
 
 #ifdef XDP_USE_NEED_WAKEUP
-static int
-rx_syscall_needed(struct xsk_ring_prod *q, uint32_t busy_budget)
+static void
+rx_syscall_handler(struct xsk_ring_prod *q, uint32_t busy_budget,
+		   struct pollfd *fds, struct xsk_socket *xsk)
 {
-	return xsk_ring_prod__needs_wakeup(q) | busy_budget;
+	/* we can assume a kernel >= 5.11 is in use if busy polling is enabled
+	 * and thus we can safely use the recvfrom() syscall which is only
+	 * supported for AF_XDP sockets in kernels >= 5.11.
+	 */
+	if (busy_budget) {
+		(void)recvfrom(xsk_socket__fd(xsk), NULL, 0,
+			MSG_DONTWAIT, NULL, NULL);
+		return;
+	}
+
+	if (xsk_ring_prod__needs_wakeup(q))
+		(void)poll(fds, 1, 1000);
 }
 static int
 tx_syscall_needed(struct xsk_ring_prod *q)
@@ -52,10 +65,13 @@ tx_syscall_needed(struct xsk_ring_prod *q)
 	return xsk_ring_prod__needs_wakeup(q);
 }
 #else
-static int
-rx_syscall_needed(struct xsk_ring_prod *q __rte_unused, uint32_t busy_budget)
+static void
+rx_syscall_handler(struct xsk_ring_prod *q __rte_unused, uint32_t busy_budget,
+		   struct pollfd *fds __rte_unused, struct xsk_socket *xsk)
 {
-	return busy_budget;
+	if (busy_budget)
+		(void)recvfrom(xsk_socket__fd(xsk), NULL, 0,
+			MSG_DONTWAIT, NULL, NULL);
 }
 static int
 tx_syscall_needed(struct xsk_ring_prod *q __rte_unused)
diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c b/drivers/net/af_xdp/rte_eth_af_xdp.c
index 8c6cd224a8..0c91a40c4a 100644
--- a/drivers/net/af_xdp/rte_eth_af_xdp.c
+++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
@@ -5,7 +5,6 @@
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>
-#include <poll.h>
 #include <netinet/in.h>
 #include <net/if.h>
 #include <sys/socket.h>
@@ -273,10 +272,8 @@ af_xdp_rx_zc(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 	nb_pkts = xsk_ring_cons__peek(rx, nb_pkts, &idx_rx);
 
 	if (nb_pkts == 0) {
-		if (rx_syscall_needed(&rxq->fq, rxq->busy_budget))
-			(void)recvfrom(xsk_socket__fd(rxq->xsk), NULL, 0,
-				MSG_DONTWAIT, NULL, NULL);
-
+		rx_syscall_handler(&rxq->fq, rxq->busy_budget, &rxq->fds[0],
+				   rxq->xsk);
 		return 0;
 	}
 
@@ -346,8 +343,7 @@ af_xdp_rx_cp(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 	if (nb_pkts == 0) {
 #if defined(XDP_USE_NEED_WAKEUP)
 		if (xsk_ring_prod__needs_wakeup(fq))
-			(void)recvfrom(xsk_socket__fd(rxq->xsk), NULL, 0,
-				MSG_DONTWAIT, NULL, NULL);
+			(void)poll(rxq->fds, 1, 1000);
 #endif
 		return 0;
 	}