From: Vinicius Costa Gomes <vinicius.go...@intel.com> Add some pointers to the definition of the CBS algorithm, and some notes about the limits of its implementation in the i210 family of controllers.
Signed-off-by: Vinicius Costa Gomes <vinicius.go...@intel.com> Tested-by: Aaron Brown <aaron.f.br...@intel.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirs...@intel.com> --- .../networking/device_drivers/intel/igb.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/networking/device_drivers/intel/igb.rst b/Documentation/networking/device_drivers/intel/igb.rst index ba16b86d5593..e87a4a72ea2d 100644 --- a/Documentation/networking/device_drivers/intel/igb.rst +++ b/Documentation/networking/device_drivers/intel/igb.rst @@ -177,6 +177,25 @@ rate limit using the IProute2 tool. Download the latest version of the IProute2 tool from Sourceforge if your version does not have all the features you require. +Credit Based Shaper (Qav Mode) +------------------------------ +When enabling the CBS qdisc in the hardware offload mode, traffic shaping using +the CBS (described in the IEEE 802.1Q-2018 Section 8.6.8.2 and discussed in the +Annex L) algorithm will run in the i210 controller, so it's more accurate and +uses less CPU. + +When using offloaded CBS, and the traffic rate obeys the configured rate +(doesn't go above it), CBS should have little to no effect in the latency. + +The offloaded version of the algorithm has some limits, caused by how the idle +slope is expressed in the adapter's registers. It can only represent idle slopes +in 16.38431 kbps units, which means that if a idle slope of 2576kbps is +requested, the controller will be configured to use a idle slope of ~2589 kbps, +because the driver rounds the value up. For more details, see the comments on +:c:func:`igb_config_tx_modes()`. + +NOTE: This feature is exclusive to i210 models. + Support ======= -- 2.19.2
