[SDFAB-595] Add queues configuration
Change-Id: I0f8e0fdd058c41da8262690142051723601006e4
diff --git a/advanced/qos.rst b/advanced/qos.rst
index 4310e8e..27a7aeb 100644
--- a/advanced/qos.rst
+++ b/advanced/qos.rst
@@ -1,2 +1,129 @@
QoS and Slicing
===============
+
+.. _qos_configuration:
+
+Configuration
+-------------
+.. note:: QoS and slicing configuration is currently statically configured at switch startup.
+ Dynamic configuration will be supported in a next SD-Fabric release.
+
+QoS and Slicing is configured via the ``vendor_config`` portion of the Stratum Chassis Config (see :ref:`stratum_chassis_config`),
+where the queues and schedulers can be configured.
+We provide a convenient `script <https://github.com/stratum/fabric-tna/blob/main/util/gen-stratum-qos-config.py>`_
+to generate the configuration starting from a higher-level description provided via a YAML file.
+This file allows to configure the parameters for the traffic classes listed in the previous sections.
+
+Here's a list of parameters that you can configure via the YAML QoS configuration file:
+
+* ``max_cells``: Maximum number of buffer cells, depends on the ASIC SKU/revision.
+
+* ``pool_allocations``: Percentage of buffer cells allocated to each traffic class.
+ The sum should be 100. Usually, we leave a portion of the buffer ``unassigned``
+ for queues that do not have a pool (yet).
+ Example of such queues are those for the recirculation port, CPU port, etc.
+
+ .. code-block:: yaml
+
+ pool_allocations:
+ control: 1
+ realtime: 9
+ elastic: 80
+ besteffort: 9
+ unassigned: 1
+
+* **Control** Traffic Class: The available bandwidth dedicated to Control traffic is divided in *slots*.
+ Each slot has a maximum rate and burst (in packets of the given MTU).
+ A slice can use one or more slots by appropriately configuring meters in the fabric ingress pipeline.
+
+ * ``control_slot_count``: Number of slots.
+ * ``control_slot_rate_pps``: Packet per second rate of each slot.
+ * ``control_slot_burst_pkts``: Number of packets per burst of each slot.
+ * ``control_mtu_bytes``: MTU of packets for the PPS and burst values.
+
+ .. code-block:: yaml
+
+ control_slot_count: 50
+ control_slot_rate_pps: 100
+ control_slot_burst_pkts: 10
+ control_mtu_bytes: 1500
+
+* **Real-Time** Traffic Class Configuration:
+
+ * ``realtime_max_rates_bps``: List of maximum shaping rates for Real-Time queues,
+ one per slice requesting such service.
+
+ * ``realtime_max_burst_s``: Maximum amount of time that a Real-Time queue can
+ burst at the port speed. This parameter is used to limit delay for Elastic
+ queues.
+
+ .. code-block:: yaml
+
+ realtime_max_rates_bps:
+ - 45000000 # 45 Mbps
+ - 30000000 # 30 Mbps
+ - 25000000 # 25 Mbps
+ realtime_max_burst_s: 0.005 # 5 ms
+
+* **Elastic** Traffic Class Configuration:
+
+ * ``elastic_min_rates_bps``: List of minimum guaranteed rates for Elastic queues,
+ one per slice requesting such service.
+
+ .. code-block:: yaml
+
+ elastic_min_rates_bps:
+ - 100000000 # 100 Mbps
+ - 200000000 # 200 Mbps
+
+* ``port_templates`` section: List of switch port for which we want to configure
+ queues.
+
+ Every ``port_templates`` element contains:
+
+ * ``descr``: Description of the port purpose.
+
+ * ``rate_bps``: Port speed in bit per second.
+
+ * ``is_shaping_enabled``: ``true`` if the rate is enforced using shaping,
+ ``false`` if the rate is the channel speed.
+
+ * ``shaping_burst_bytes``: Burst size in bytes, meaningful only if port speed
+ is shaped (when ``is_shaping_enabled: true``).
+
+ * ``queue_count``: Number of queues assigned to the port.
+
+ * ``port_ids``: List of Stratum port IDs (:ref:`singleton_port` from Stratum Chassis Config),
+ using this port template. Used for port that corresponds to switch front-panel ports.
+
+ Mutually exclusive with ``sdk_port_ids`` field.
+
+ * ``sdk_port_ids``: List of SDK port numbers (i.e., Tofino DP_ID) using this port template.
+ Used for internal ports (e.g., recirculation ports).
+
+ Mutually exclusive with ``port_ids`` field.
+
+ .. code-block:: yaml
+
+ port_templates:
+ - descr: "Base station"
+ rate_bps: 1000000000 # 1 Gbps
+ is_shaping_enabled: true
+ shaping_burst_bytes: 18000 # 2x jumbo frames
+ queue_count: 16
+ port_ids:
+ - 100
+ - descr: "Servers"
+ port_ids:
+ - 200
+ rate_bps: 40000000000 # 40 Gbps
+ is_shaping_enabled: false
+ queue_count: 16
+ - descr: "Recirculation"
+ sdk_port_ids:
+ - 68
+ rate_bps: 100000000000 # 100 Gbps
+ is_shaping_enabled: false
+ queue_count: 16
+
+An example of a complete QoS and Slicing configuration can be found `here <https://github.com/stratum/fabric-tna/blob/main/util/sample-qos-config.yaml>`_.