Hello,

I noticed a small inconsistency in the virtio pmd's xstats.
The stat "rx_q0_errors" appears twice.
I also think the stats "rx_q0_packets", "rx_q0_bytes", "tx_q0_packets" and
"tx_q0_bytes" are duplicates of "rx_q0_good_packets", "rx_q0_good_bytes",
"tx_q0_good_packets" and "tx_q0_good_bytes"

I believe this issue probably appeared after this commit:

f30e69b41f94: ethdev: add device flag to bypass auto-filled queue xstats
http://scm.6wind.com/vendor/dpdk.org/dpdk/commit/?id=f30e69b41f949cd4a9afb6ff39de196e661708e2

From what I understand, the rxq0_error stat was originally reported by the
librte. However, changes were made so it is reported by the pmd instead.
The flag RTE_ETH_DEV_AUTOFILL_QUEUE_XSTATS was temporarily set to keep the
old behaviour so that every pmd could have time to adapt the change.
But it seems the flag was forgotten in the virtio pmd and as a result, some
stats are fetched at two different times when displaying xstats.

First in lib_rte_ethdev:
https://git.dpdk.org/dpdk/tree/lib/ethdev/rte_ethdev.c#n3266
(you can see the check on the RTE_ETH_DEV_AUTOFILL_QUEUE_XSTATS flag before
the snprintf on eth_dev_rxq_stats_strings[] )

And a second time in the virtio pmd:
https://git.dpdk.org/dpdk/tree/drivers/net/virtio/virtio_ethdev.c#n705 pmd
(see the snprintf on rte_virtio_rxq_stat_strings[] )

This problem can be reproduced on testpmd simply by displaying the xstats
on a port with the net_virtio driver:

Reproduction:
===========

    1) start dpdk-testpmd:

modprobe -a uio_pci_generic
dpdk-devbind -b uio_pci_generic 03:00.0
dpdk-devbind -b uio_pci_generic 04:00.0

dpdk-devbind -s

Network devices using DPDK-compatible driver
============================================
0000:03:00.0 'Virtio 1.0 network device 1041' drv=uio_pci_generic
unused=vfio-pci
0000:04:00.0 'Virtio 1.0 network device 1041' drv=uio_pci_generic
unused=vfio-pci
[...]

dpdk-testpmd -a 0000:03:00.0 -a 0000:04:00.0 -- -i --rxq=1 --txq=1
--coremask=0x4 --total-num-mbufs=250000
EAL: Detected CPU lcores: 3
EAL: Detected NUMA nodes: 1
EAL: Detected static linkage of DPDK
EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
EAL: Selected IOVA mode 'PA'
EAL: VFIO support initialized
EAL: Probe PCI driver: net_virtio (1af4:1041) device: 0000:03:00.0 (socket
-1)
EAL: Probe PCI driver: net_virtio (1af4:1041) device: 0000:04:00.0 (socket
-1)
Interactive-mode selected
Warning: NUMA should be configured manually by using --port-numa-config and
--ring-numa-config parameters along with --numa.
testpmd: create a new mbuf pool <mb_pool_0>: n=250000, size=2176, socket=0
testpmd: preferred mempool ops selected: ring_mp_mc
Configuring Port 0 (socket 0)
Port 0: 52:54:00:B0:8F:88
Configuring Port 1 (socket 0)
Port 1: 52:54:00:EF:09:1F
Checking link statuses...
Done

    2) port info:

show port info 0

********************* Infos for port 0  *********************
MAC address: 52:54:00:B0:8F:88
Device name: 0000:03:00.0
Driver name: net_virtio
Firmware-version: not available
Devargs:
Connect to socket: 0
memory allocation on the socket: 0
Link status: up
Link speed: Unknown
Link duplex: full-duplex
Autoneg status: On
MTU: 1500
Promiscuous mode: enabled
Allmulticast mode: disabled
Maximum number of MAC addresses: 64
Maximum number of MAC addresses of hash filtering: 0
VLAN offload:
  strip off, filter off, extend off, qinq strip off
No RSS offload flow type is supported.
Minimum size of RX buffer: 64
Maximum configurable length of RX packet: 9728
Maximum configurable size of LRO aggregated packet: 0
Current number of RX queues: 1
Max possible RX queues: 1
Max possible number of RXDs per queue: 32768
Min possible number of RXDs per queue: 32
RXDs number alignment: 1
Current number of TX queues: 1
Max possible TX queues: 1
Max possible number of TXDs per queue: 32768
Min possible number of TXDs per queue: 32
TXDs number alignment: 1
Max segment number per packet: 65535
Max segment number per MTU/TSO: 65535
Device capabilities: 0x0( )
Device error handling mode: none
Device private info:
guest_features: 0x110af8020
vtnet_hdr_size: 12
use_vec: rx-0 tx-0
use_inorder: rx-0 tx-0
intr_lsc: 1
max_mtu: 9698
max_rx_pkt_len: 1530
max_queue_pairs: 1
req_guest_features: 0x8000005f10ef8028

    3) show port xstats:

show port xstats 0
###### NIC extended statistics for port 0
rx_good_packets: 0
tx_good_packets: 0
rx_good_bytes: 0
tx_good_bytes: 0
rx_missed_errors: 0
rx_errors: 0
tx_errors: 0
rx_mbuf_allocation_errors: 0
rx_q0_packets: 0
rx_q0_bytes: 0
rx_q0_errors: 0      <==================
tx_q0_packets: 0
tx_q0_bytes: 0
rx_q0_good_packets: 0
rx_q0_good_bytes: 0
rx_q0_errors: 0      <==================
rx_q0_multicast_packets: 0
rx_q0_broadcast_packets: 0
rx_q0_undersize_packets: 0
rx_q0_size_64_packets: 0
rx_q0_size_65_127_packets: 0
rx_q0_size_128_255_packets: 0
rx_q0_size_256_511_packets: 0
rx_q0_size_512_1023_packets: 0
rx_q0_size_1024_1518_packets: 0
rx_q0_size_1519_max_packets: 0
tx_q0_good_packets: 0
tx_q0_good_bytes: 0
tx_q0_multicast_packets: 0
tx_q0_broadcast_packets: 0
tx_q0_undersize_packets: 0
tx_q0_size_64_packets: 0
tx_q0_size_65_127_packets: 0
tx_q0_size_128_255_packets: 0
tx_q0_size_256_511_packets: 0
tx_q0_size_512_1023_packets: 0
tx_q0_size_1024_1518_packets: 0
tx_q0_size_1519_max_packets: 0

You can see the stat "rx_q0_errors" appeared twice.