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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>`_.