[PATCH 20.11] net/af_packet: fix ignoring full ring on Tx

[Xueming(Steven) Li]

On Thu, 2021-11-11 at 11:40 +0200, Tudor Cornea wrote:
> [ upstream commit f86d553cc180f9a65e115edb5641a49bbf2cf2f0 ]
> 
> 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>
> ---

Applied to 20.11.4 list, thanks!