From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vinicius Costa Gomes Subject: [next-queue PATCH v1 2/2] Documentation: igb: Add a section about CBS Date: Fri, 16 Nov 2018 16:19:24 -0800 Message-ID: <20181117001924.1525-2-vinicius.gomes@intel.com> References: <20181117001924.1525-1-vinicius.gomes@intel.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Cc: Vinicius Costa Gomes , jeffrey.t.kirsher@intel.com, netdev@vger.kernel.org, jesus.s.palencia@gmail.com To: intel-wired-lan@lists.osuosl.org Return-path: Received: from mga14.intel.com ([192.55.52.115]:39175 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729736AbeKQKfL (ORCPT ); Sat, 17 Nov 2018 05:35:11 -0500 In-Reply-To: <20181117001924.1525-1-vinicius.gomes@intel.com> Sender: netdev-owner@vger.kernel.org List-ID: 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 --- Documentation/networking/igb.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/networking/igb.rst b/Documentation/networking/igb.rst index ba16b86d5593..e87a4a72ea2d 100644 --- a/Documentation/networking/igb.rst +++ b/Documentation/networking/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 ======= -- 2.19.1