21. FM10K Poll Mode Driver

The FM10K poll mode driver library provides support for the Intel FM10000 (FM10K) family of 40GbE/100GbE adapters.

21.1. FTAG Based Forwarding of FM10K

FTAG Based Forwarding is a unique feature of FM10K. The FM10K family of NICs support the addition of a Fabric Tag (FTAG) to carry special information. The FTAG is placed at the beginning of the frame, it contains information such as where the packet comes from and goes, and the vlan tag. In FTAG based forwarding mode, the switch logic forwards packets according to glort (global resource tag) information, rather than the mac and vlan table. Currently this feature works only on PF.

To enable this feature, the user should pass a devargs parameter to the eal like “-a 84:00.0,enable_ftag=1”, and the application should make sure an appropriate FTAG is inserted for every frame on TX side.

21.2. Vector PMD for FM10K

Vector PMD (vPMD) uses Intel® SIMD instructions to optimize packet I/O. It improves load/store bandwidth efficiency of L1 data cache by using a wider SSE/AVX ‘’register (1)’‘. The wider register gives space to hold multiple packet buffers so as to save on the number of instructions when bulk processing packets.

There is no change to the PMD API. The RX/TX handlers are the only two entries for vPMD packet I/O. They are transparently registered at runtime RX/TX execution if all required conditions are met.

Some constraints apply as pre-conditions for specific optimizations on bulk packet transfers. The following sections explain RX and TX constraints in the vPMD.

21.2.1. RX Constraints

21.2.1.1. Prerequisites and Pre-conditions

For Vector RX it is assumed that the number of descriptor rings will be a power of 2. With this pre-condition, the ring pointer can easily scroll back to the head after hitting the tail without a conditional check. In addition Vector RX can use this assumption to do a bit mask using ring_size - 1.

21.2.1.2. Features not Supported by Vector RX PMD

Some features are not supported when trying to increase the throughput in vPMD. They are:

  • IEEE1588
  • Flow director
  • Header split
  • RX checksum offload

Other features are supported using optional MACRO configuration. They include:

  • HW VLAN strip
  • L3/L4 packet type

To enable via RX_OLFLAGS use RTE_LIBRTE_FM10K_RX_OLFLAGS_ENABLE=y.

To guarantee the constraint, the following capabilities in dev_conf.rxmode.offloads will be checked:

  • RTE_ETH_RX_OFFLOAD_VLAN_EXTEND
  • RTE_ETH_RX_OFFLOAD_CHECKSUM
  • RTE_ETH_RX_OFFLOAD_HEADER_SPLIT
  • fdir_conf->mode

21.2.1.3. RX Burst Size

As vPMD is focused on high throughput, it processes 4 packets at a time. So it assumes that the RX burst should be greater than 4 packets per burst. It returns zero if using nb_pkt < 4 in the receive handler. If nb_pkt is not a multiple of 4, a floor alignment will be applied.

21.2.2. TX Constraint

21.2.2.1. Features not Supported by TX Vector PMD

TX vPMD only works when offloads is set to 0

This means that it does not support any TX offload.

21.3. Limitations

21.3.1. Switch manager

The Intel FM10000 family of NICs integrate a hardware switch and multiple host interfaces. The FM10000 PMD only manages host interfaces. For the switch component another switch driver has to be loaded prior to the FM10000 PMD. The switch driver can be acquired from Intel support. Only Testpoint is validated with DPDK, the latest version that has been validated with DPDK is 4.1.6.

21.3.2. Support for Switch Restart

For FM10000 multi host based design a DPDK app running in the VM or host needs to be aware of the switch’s state since it may undergo a quit-restart. When the switch goes down the DPDK app will receive a LSC event indicating link status down, and the app should stop the worker threads that are polling on the Rx/Tx queues. When switch comes up, a LSC event indicating LINK_UP is sent to the app, which can then restart the FM10000 port to resume network processing.

21.3.3. CRC stripping

The FM10000 family of NICs strip the CRC for every packets coming into the host interface. So, keeping CRC is not supported.

21.3.4. Maximum packet length

The FM10000 family of NICS support a maximum of a 15K jumbo frame. The value is fixed and cannot be changed. So, even when the rxmode.mtu member of struct rte_eth_conf is set to a value lower than 15364, frames up to 15364 bytes can still reach the host interface.

21.3.5. Statistic Polling Frequency

The FM10000 NICs expose a set of statistics via the PCI BARs. These statistics are read from the hardware registers when rte_eth_stats_get() or rte_eth_xstats_get() is called. The packet counting registers are 32 bits while the byte counting registers are 48 bits. As a result, the statistics must be polled regularly in order to ensure the consistency of the returned reads.

Given the PCIe Gen3 x8, about 50Gbps of traffic can occur. With 64 byte packets this gives almost 100 million packets/second, causing 32 bit integer overflow after approx 40 seconds. To ensure these overflows are detected and accounted for in the statistics, it is necessary to read statistic regularly. It is suggested to read stats every 20 seconds, which will ensure the statistics are accurate.

21.3.6. Interrupt mode

The FM10000 family of NICS need one separate interrupt for mailbox. So only drivers which support multiple interrupt vectors e.g. vfio-pci can work for fm10k interrupt mode.