User Manual

Rev 2.1-1.0.6

Mellanox Technologies

4.4 Quality of Service InfiniBand

4.4.1 Quality of Service Overview

Quality of Service (QoS) requirements stem from the realization of I/O consolidation over an IB

network. As multiple applications and ULPs share the same fabric, a means is needed to control

their use of network resources.

Figure 2: I/O Consolidation Over InfiniBand

QoS over Mellanox OFED for Linux is discussed in Chapter 8, “OpenSM – Subnet Manager”.

The basic need is to differentiate the service levels provided to different traffic flows, such that a

policy can be enforced and can control each flow utilization of fabric resources.

The InfiniBand Architecture Specification defines several hardware features and management

interfaces for supporting QoS:

• Up to 15 Virtual Lanes (VL) carry traffic in a non-blocking manner

• Arbitration between traffic of different VLs is performed by a two-priority-level

weighted round robin arbiter. The arbiter is programmable with a sequence of (VL,

weight) pairs and a maximal number of high priority credits to be processed before low

priority is served

• Packets carry class of service marking in the range 0 to 15 in their header SL field

• Each switch can map the incoming packet by its SL to a particular output VL, based on

a programmable table VL=SL-to-VL-MAP(in-port, out-port, SL)

• The Subnet Administrator controls the parameters of each communication flow by pro-

viding them as a response to Path Record (PR) or MultiPathRecord (MPR) queries

DiffServ architecture (IETF RFC 2474 & 2475) is widely used in highly dynamic fabrics. The

following subsections provide the functional definition of the various software elements that

enable a DiffServ-like architecture over the Mellanox OFED software stack.