Patch fix from https://github.com/DPDK/dpdk/commit/a08f9cb698c3d4687765860e328dca727f7a516b
For Rx-Queue Interrupt Setting, when VF Rx interrupt

disable (INTENA=0), there are two ways to write back

descriptor to host memory:
1) Set WB_ON_ITR bit 0 to Interrupt Dynamic Control Register:

Completed descriptors are posted to host memory according to

the internal descriptor cache policy (in other words when a

full cache line is available for write-back).
A internal descriptor size is 16 bytes or 32 bytes, a cache

line size is 64 bytes or 128 bytes from datasheet :

PCIe Global Config 2 - GLPCI_CNF2 (0x000BE004; RO)

so the full cache line could contains 4 packets, it means

Network card will send 4 packets to host when a full cache line

is available.
2) Set WB_ON_ITR bit 1 to Interrupt Dynamic Control Register:

Completed descriptors also trigger the ITR. Following ITR

expiration, all leftover completed descriptors are posted to

host memory.
Network card will send packet to host even if only one

descriptor is completed.
Changing 1) to 2) to make sure VF send the packet to host even

if there is only one Rx packet is ready in hardware.

AN(config)#system tune rxmode interrupt
AN(config)#ping 192.168.1.104

PING 192.168.1.104 (192.168.1.104) 56(84) bytes of data.

64 bytes from 192.168.1.104: icmp_seq=1 ttl=64 time=2.30 ms

64 bytes from 192.168.1.104: icmp_seq=2 ttl=64 time=1.51 ms

64 bytes from 192.168.1.104: icmp_seq=3 ttl=64 time=2.11 ms

64 bytes from 192.168.1.104: icmp_seq=4 ttl=64 time=1.48 ms

64 bytes from 192.168.1.104: icmp_seq=5 ttl=64 time=1.98 ms
--- 192.168.1.104 ping statistics ---

5 packets transmitted, 5 received, 0% packet loss, time 4004ms

rtt min/avg/max/mdev = 1.484/1.880/2.301/0.327 ms
AN(config)#system tune rxmode poll 100
AN#ping 192.168.1.104

PING 192.168.1.104 (192.168.1.104) 56(84) bytes of data.

64 bytes from 192.168.1.104: icmp_seq=1 ttl=64 time=0.784 ms

64 bytes from 192.168.1.104: icmp_seq=2 ttl=64 time=0.892 ms

64 bytes from 192.168.1.104: icmp_seq=3 ttl=64 time=0.822 ms

64 bytes from 192.168.1.104: icmp_seq=4 ttl=64 time=0.717 ms

64 bytes from 192.168.1.104: icmp_seq=5 ttl=64 time=0.711 ms
--- 192.168.1.104 ping statistics ---

5 packets transmitted, 5 received, 0% packet loss, time 4000ms

rtt min/avg/max/mdev = 0.711/0.785/0.892/0.069 ms