SMFS and DMFS in Hardware Offloading

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SMFS and DMFS in Hardware Offloading

switchdev (ethernet switch device driver model)

kernel.org - switchdev

The Ethernet switch device driver model (switchdev) is an in-kernel driver model for switch devices which offload the forwarding (data) plane from the kernel.

Configuration

  1. Use “depends NET_SWITCHDEV” in driver’s Kconfig to ensure switchdev model support is built for driver.
  2. use devlink tool to setup switch mode devlink dev eswitch set pci/$PF_PCI mode switchdev

switchdev Performance Tuning

OVS Offload Using ASAP2 Direct

SwitchDev proformance can be furtuer improved by tuning it.

Steering Mode

OVS-kernel supports two steering modes for rules insertion into hardware.

  1. SMFS – Software Managed Flow Steering (as of MLNX_OFED v5.1, this is the default mode)
    Rules are inserted directly to the hardrware by the software (driver). This mode is optimized for rules insertion.
  2. DMFS – Device Managed Flow Steering
    Rules insertion is done using firmware commands. This mode is optimized for throughput with a small amount of rules in the system.

Configuration

The mode can be controlled via sysfs or devlink API in kernels that support it:

Sysfs:

# echo smfs > /sys/class/net/<PF netdev>/compat/devlink/steering_mode

Devlink:

# devlink dev param set pci/0000:00:08.0 name flow_steering_mode value "smfs" cmode runtime

Replace smfs param with dmfs for device managed flow steering

Notes

  • SMFS and DMFS mode should be set before moving the device to “switchdev” mode.
  • Only when moving to SwitchDev will the driver use the mode set by the previous step.
  • Steering mode cannot be changed after moving to “switchdev” mode
  • Steering mode can only be applicable for “switchdev” mode only, which means no effects to legacy SR-IOV or other configurations.