|author||Vinicius Costa Gomes <email@example.com>||2018-11-16 16:19:24 -0800|
|committer||Jeff Kirsher <firstname.lastname@example.org>||2018-12-20 11:50:54 -0800|
|parent||igb: Change RXPBSIZE size when setting Qav mode (diff)|
Documentation: igb: Add a section about CBS
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 <email@example.com> Tested-by: Aaron Brown <firstname.lastname@example.org> Signed-off-by: Jeff Kirsher <email@example.com>
1 files changed, 19 insertions, 0 deletions
diff --git a/Documentation/networking/device_drivers/intel/igb.rst b/Documentation/networking/device_drivers/intel/igb.rst
index ba16b86d5593..e87a4a72ea2d 100644
@@ -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
+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 220.127.116.11 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
+NOTE: This feature is exclusive to i210 models.