All RX packets are counted as rx_missed_errors in software or service mode when using DPDK

[akorud]

Hi,
I have a loopback setup between two ports of a dual-port Intel XXV710 25G NIC. I run the simplest tests - running the stl/udp_1pkt_simple.py profile from one port to another.
In HW mode, everything runs perfectly, up to line rate. However, as I use EMU, it should run in software mode. Here I discovered strange behavior which also happens when enabling service mode on the port.
The problem is that the first 4087 packets are received and counted as ipackets, and all following packets are counted as ierrors (rx_missed_errors). The sum of ipackets and ierrors equals the number of packets sent.
This happens only when DPDK is being used. With exactly the same interfaces in Linux mode, everything works perfectly, though the rate is limited to ~4Gbps (expected, no kernel bypass).
I tried to dig through the code and found that rx_missed_errors represents the I40E_GLPRT_RDPC register, which, among other things, counts packets discarded because the RX ring is full.
Is it possible that in software or service mode, mbufs are not reclaimed back? This would explain why only the first packets are received.
BTW, capture also doesn't work, even with service mode enabled, 0 packets are being captured.

[akorud]

I was able to trace down to

    inline uint16_t  HOT_FUNC rx_burst(uint16_t queue_id, struct rte_mbuf **rx_pkts, uint16_t nb_pkts) { 

    if (likely( !m_is_dummy )) {
        return rte_eth_rx_burst(m_repid, queue_id, rx_pkts, nb_pkts);
    } else {
        return 0;
    }

and despite NIC counters are increasing (confused by rx_unknown_protocol_packets), this function doesn't receive any packets from NIC.

rx_good_packets                |               0 |             862 
tx_good_packets                |             862 |               0 
rx_good_bytes                  |               0 |          208604 
tx_good_bytes                  |          208604 |               0 
rx_unicast_packets             |               0 |             862 
rx_unknown_protocol_packets    |               0 |             862 
tx_unicast_packets             |             862 |               0 
rx_size_128_to_255_packets     |               0 |             862 
tx_size_128_to_255_packets     |             862 |               0 

I've captured that packets using mirror port and wireshark on different NIC - they are valid UDP packets.