[PATCH 19.11] net/af_packet: fix ignoring full ring on Tx
Christian Ehrhardt
christian.ehrhardt at canonical.com
Wed Dec 1 16:38:29 CET 2021
On Wed, Dec 1, 2021 at 12:02 PM Tudor Cornea <tudor.cornea at gmail.com> wrote:
>
> [ upstream commit f86d553cc180f9a65e115edb5641a49bbf2cf2f0 ]
Thanks, applied
> 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")
>
> 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>
> ---
> 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 00387ed..dbbe8e5 100644
> --- a/drivers/net/af_packet/rte_eth_af_packet.c
> +++ b/drivers/net/af_packet/rte_eth_af_packet.c
> @@ -213,8 +213,30 @@ eth_af_packet_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
> }
>
> /* point at the next incoming frame */
> - if ((ppd->tp_status != TP_STATUS_AVAILABLE) &&
> - (poll(&pfd, 1, -1) < 0))
> + if (ppd->tp_status != TP_STATUS_AVAILABLE) {
> + 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 (ppd->tp_status != TP_STATUS_AVAILABLE)
> break;
>
> /* copy the tx frame data */
> --
> 2.7.4
>
--
Christian Ehrhardt
Staff Engineer, Ubuntu Server
Canonical Ltd
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