15. IXGBE Driver

15.1.1. RX Constraints

15.1.2. TX Constraint

15.3.1. l3fwd

When running l3fwd with vPMD, there is one thing to note. In the configuration, ensure that port_conf.rxmode.hw_ip_checksum=0. Otherwise, by default, RX vPMD is disabled.

15.3.2. load_balancer

As in the case of l3fwd, set configure port_conf.rxmode.hw_ip_checksum=0 to enable vPMD. In addition, for improved performance, use -bsz “(32,32),(64,64),(32,32)” in load_balancer to avoid using the default burst size of 144.

15.4.1. Malicious Driver Detection not Supported

The Intel x550 series NICs support a feature called MDD (Malicious Driver Detection) which checks the behavior of the VF driver. If this feature is enabled, the VF must use the advanced context descriptor correctly and set the CC (Check Context) bit. DPDK PF doesn’t support MDD, but kernel PF does. We may hit problem in this scenario kernel PF + DPDK VF. If user enables MDD in kernel PF, DPDK VF will not work. Because kernel PF thinks the VF is malicious. But actually it’s not. The only reason is the VF doesn’t act as MDD required. There’s significant performance impact to support MDD. DPDK should check if the advanced context descriptor should be set and set it. And DPDK has to ask the info about the header length from the upper layer, because parsing the packet itself is not acceptable. So, it’s too expensive to support MDD. When using kernel PF + DPDK VF on x550, please make sure to use a kernel PF driver that disables MDD or can disable MDD.

Some kernel drivers already disable MDD by default while some kernels can use the command insmod ixgbe.ko MDD=0,0 to disable MDD. Each “0” in the command refers to a port. For example, if there are 6 ixgbe ports, the command should be changed to insmod ixgbe.ko MDD=0,0,0,0,0,0.

15.4.2. Statistics

The statistics of ixgbe hardware must be polled regularly in order for it to remain consistent. Running a DPDK application without polling the statistics will cause registers on hardware to count to the maximum value, and “stick” at that value.

In order to avoid statistic registers every reaching the maximum value, read the statistics from the hardware using rte_eth_stats_get() or rte_eth_xstats_get().

The maximum time between statistics polls that ensures consistent results can be calculated as follows:

max_read_interval = UINT_MAX / max_packets_per_second
max_read_interval = 4294967295 / 14880952
max_read_interval = 288.6218096127183 (seconds)
max_read_interval = ~4 mins 48 sec.

In order to ensure valid results, it is recommended to poll every 4 minutes.

15.4.3. MTU setting

Although the user can set the MTU separately on PF and VF ports, the ixgbe NIC only supports one global MTU per physical port. So when the user sets different MTUs on PF and VF ports in one physical port, the real MTU for all these PF and VF ports is the largest value set. This behavior is based on the kernel driver behavior.