[dpdk-users] packet drops seen once the no of rxd pkts reach the ring size

[Gaurav Bansal]

Hi all,
I am using dpdk 16.04 library to process the packets on a vmware vm (say
vm1). The traffic is sent through a client machine using apache bench. I am
observing an issue when the number of packets reaching the vmxnet3
interface reaches the descriptor ring size (set to 2048). Till 2048 all the
packets correctly reach the 'vmxnet3_recv_pkts' function.

But as the number of packets received reaches 2048, i start seeing some
retransmissions on the client side (as shown by tcpdump on client side).
Then i captured the packets on the esx host destined to vm1 and it shows
that all the original packets as well as the corresponding retransmissions
are reaching vm1. But somehow these packets fail to reach till
'vmxnet3_recv_pkts' function (this was found by putting the breakpoint in
'vmxnet3_recv_pkts' function and dumping the packet contents, which showed
that some packets don't reach here).

Now 'vmxnet3_recv_pkts' is the first function which reads the packets from
the descriptor ring and as the packets are not reaching till here, i am not
sure on how to debug this further. Possibly some issues related to the ring
initialization.... I enabled the init & RX logs for vmxnet3, but i don't
see any error logs as well. I also tried looking at rxq stats and it shows
0 all the time :
(gdb) p rxq->stats
$1 = {drop_total = 0, drop_err = 0, drop_fcs = 0, rx_buf_alloc_failure = 0}

Can anyone please provide some clues on how to debug this further ? Are
there any known issues related to this which have been fixed post 16.04
version ?
thanks,
gaurav