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net/af_packet: fix ignoring full ring on Tx

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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>
This commit is contained in:
Tudor Cornea 2021-11-02 17:47:24 +02:00 committed by Ferruh Yigit
parent b75d85b766
commit f86d553cc1
1 changed files with 24 additions and 2 deletions
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26
drivers/net/af_packet/rte_eth_af_packet.c
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@ -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 */