[dpdk-dev] [PATCH 2/2] net/af_xdp: only use recvfrom if busy polling is enabled

[Ciara Loftus]

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.lof...@intel.com>
---
 drivers/net/af_xdp/compat.h         | 28 ++++++++++++++++++++++------
 drivers/net/af_xdp/rte_eth_af_xdp.c | 10 +++-------
 2 files changed, 25 insertions(+), 13 deletions(-)

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;
        }
-- 
2.25.1