Understanding The Subnet Manager (Sm) - HP zl User Manual

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The Queue Pair (QP) is one of the primary architectural elements of InfiniBand. In InfiniBand,
communication occurs between Queue Pairs, instead of between ports.
A Queue Pair (QP) in an addressable entity, and consists of two Work Queues: 1). Send Work Queue
and a 2). Receive Work Queue. (A work queue provides a verb consumer with the ability to queue up a
set of instructions that are executed by the Channel Adapter.) The Channel Adapter hardware takes over
the task of arbitrating communication - multiplexing access to the send queue or de-multiplexing
messages on the receive queue.
A connection is made by linking a local queue pair to a remote queue pair. Applications do not share
queue pairs; therefore, once you set them up, you can manage them at the application level without
incurring the overhead of system calls.
Send and Receive work queues are:
• always created as a pair
• always remain a pair
• known as Queue Pairs
• identified by a Queue Pair number, which is within the Channel Adapter.
Queue pairs have:
• a region of memory to be used as buffers (numbers of Queue Pairs are only limited by memory).
• a key that must match on each incoming packet (the Q_Key) to verify the validity of the packet
• (potentially) a partition key, which specifies the portion of the fabric that this queue pair may
access.
The queue pair is the mechanism by which you define quality of service, system protection, error
detection and response, and allowable services.
Types of Services
Each queue pair is independently configured for a particular type of service. These service types
provide different levels of service and different error-recovery characteristics.
The available transport-service types include:
• Reliable connection
• Unreliable connection
• Reliable Datagram
• Unreliable Datagram
Once the fabric connections are discovered, queue pairs and protection domains are established, and the
type and quality of service are defined for each queue pair, the fabric operates reliably and securely at
full performance without impact on system hardware or software resources.

Understanding the Subnet Manager (SM)

The Subnet Manager configures and maintains fabric operations. There can be multiple Subnet
Managers, but only one master.
For information regarding configuring the subnet managers, refer to
Through the GUI" on page 61
The Subnet Manager is the central repository of all information that is required to setup and bring up the
InfiniBand fabric.
The master Subnet Manager
• Discovers the fabric topology.
• Discovers endnodes.
• Configures switches and end nodes with their parameters, such as:
or "Using the Subnet Manager Through the CLI" on page
"Using the Subnet Manager
81.