User Manual

Driver FeaturesRev 2.2-1.0.1

Mellanox Technologies

4.5.5 OpenSM Features

The QoS related functionality that is provided by OpenSM—the Subnet Manager described in

Chapter 8 can be split into two main parts:

I. Fabric Setup

During fabric initialization, the Subnet Manager parses the policy and apply its settings to the

discovered fabric elements.

II. PR/MPR Query Handling

OpenSM enforces the provided policy on client request. The overall flow for such requests is:

first the request is matched against the defined match rules such that the target QoS-Level defini

tion is found. Given the QoS-Level a path(s) search is performed with the given restrictions

imposed by that level.

4.6 Quality of Service Ethernet

4.6.1 Quality of Service Overview

Quality of Service (QoS) is a mechanism of assigning a priority to a network flow (socket,

rdma_cm connection) and manage its guarantees, limitations and its priority over other flows.

This is accomplished by mapping the user's priority to a hardware TC (traffic class) through a 2/

3 stages process. The TC is assigned with the QoS attributes and the different flows behave

accordingly

4.6.2 Mapping Traffic to Traffic Classes

Mapping traffic to TCs consists of several actions which are user controllable, some controlled

by the application itself and others by the system/network administrators.

The following is the general mapping traffic to Traffic Classes flow:

1. The application sets the required Type of Service (ToS).

2. The ToS is translated into a Socket Priority (sk_prio).

3. The sk_prio is mapped to a User Priority (UP) by the system administrator (some applica-

tions set sk_prio directly).

4. The UP is mapped to TC by the network/system administrator.

5. TCs hold the actual QoS parameters

QoS can be applied on the following types of traffic. However, the general QoS flow may vary

among them:

• Plain Ethernet - Applications use regular inet sockets and the traffic passes via the ker-

nel Ethernet driver

• RoCE - Applications use the RDMA API to transmit using QPs

• Raw Ethernet QP - Application use VERBs API to transmit using a Raw Ethernet QP

4.6.3 Plain Ethernet Quality of Service Mapping

Applications use regular inet sockets and the traffic passes via the kernel Ethernet driver.

The following is the Plain Ethernet QoS mapping flow: