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 <pogonarumihai@gmail.com>
Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>

diff --git a/drivers/net/af_packet/rte_eth_af_packet.c b/drivers/net/af_packet/rte_eth_af_packet.c
index cea7091c063973f8ccfe9b750b72aaeb43472fcb..1396f32c3dccd800d2276245829ff49ad88271e6 100644 (file)
--- 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 */