From f86d553cc180f9a65e115edb5641a49bbf2cf2f0 Mon Sep 17 00:00:00 2001 From: Tudor Cornea Date: Tue, 2 Nov 2021 17:47:24 +0200 Subject: [PATCH] net/af_packet: fix ignoring full ring on Tx The poll call can return POLLERR which is ignored, or it can return POLLOUT, even if there are no free frames in the mmap-ed area. We can account for both of these cases by re-checking if the next frame is empty before writing into it. We have attempted to reproduce this issue with pktgen-dpdk, using the following configuration. pktgen -l 1-4 -n 4 --proc-type=primary --no-pci --no-telemetry \ --no-huge -m 512 \ --vdev=net_af_packet0,iface=eth1,blocksz=16384,framesz=8192, \ framecnt=2048,qpairs=1,qdisc_bypass=0 \ -- \ -P \ -T \ -m "3.0" \ -f themes/black-yellow.theme We configure a low tx rate (~ 335 packets / second) and a small packet size, of about 300 Bytes from the pktgen CLI. set 0 size 300 set 0 rate 0.008 set 0 burst 1 start 0 After bringing the interface down, and up again, we seem to arrive in a state in which the tx rate is inconsistent, and does not recover. ifconfig eth1 down; sleep 7; ifconfig eth1 up [1] http://code.dpdk.org/pktgen-dpdk/pktgen-20.11.2/source/INSTALL.md Fixes: 364e08f2bbc0 ("af_packet: add PMD for AF_PACKET-based virtual devices") Cc: stable@dpdk.org Signed-off-by: Mihai Pogonaru Signed-off-by: Tudor Cornea Reviewed-by: Ferruh Yigit --- drivers/net/af_packet/rte_eth_af_packet.c | 26 +++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) diff --git a/drivers/net/af_packet/rte_eth_af_packet.c b/drivers/net/af_packet/rte_eth_af_packet.c index cea7091c06..1396f32c3d 100644 --- a/drivers/net/af_packet/rte_eth_af_packet.c +++ b/drivers/net/af_packet/rte_eth_af_packet.c @@ -237,8 +237,30 @@ eth_af_packet_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts) } /* point at the next incoming frame */ - if (!tx_ring_status_available(ppd->tp_status) && - poll(&pfd, 1, -1) < 0) + if (!tx_ring_status_available(ppd->tp_status)) { + if (poll(&pfd, 1, -1) < 0) + break; + + /* poll() can return POLLERR if the interface is down */ + if (pfd.revents & POLLERR) + break; + } + + /* + * poll() will almost always return POLLOUT, even if there + * are no extra buffers available + * + * This happens, because packet_poll() calls datagram_poll() + * which checks the space left in the socket buffer and, + * in the case of packet_mmap, the default socket buffer length + * doesn't match the requested size for the tx_ring. + * As such, there is almost always space left in socket buffer, + * which doesn't seem to be correlated to the requested size + * for the tx_ring in packet_mmap. + * + * This results in poll() returning POLLOUT. + */ + if (!tx_ring_status_available(ppd->tp_status)) break; /* copy the tx frame data */