[dpdk-dev] [PATCH v4] net/af_packet: fix ignoring full ring on tx

[Tudor Cornea]

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

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

---
v4:
* Updated comment regarding POLLERR
  Removed some extra details, and left notice about poll() returning
  POLLERR, in case of interface link down.
v3:
* Added check for POLLERR
* Used tx_ring_status_available() for checking TP_STATUS_AVAILABLE
---
 drivers/net/af_packet/rte_eth_af_packet.c | 12 ++++++++++--
 1 file changed, 10 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 559f5a0..dd6d165 100644
--- a/drivers/net/af_packet/rte_eth_af_packet.c
+++ b/drivers/net/af_packet/rte_eth_af_packet.c
@@ -237,8 +237,16 @@ 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;
+		}
+
+		if (!tx_ring_status_available(ppd->tp_status))
 			break;
 
 		/* copy the tx frame data */
-- 
2.7.4