5.2.4. Virtual Lane Support
Virtual Lanes (VLs) provide multiple logical flows of data over a single physical link. Virtual fabrics as well as MPI jobs specify a Service Level where traffic will be routed.
Different ports (nodes) connected in the fabric cluster can support a varying number of VLs. Generally, Omni-Path products support eight VLs, but future products may support a different number of VLs. When configuring vFabrics, every Service Level (SL) in use maps to a unique VL. This imposes a limit of SL assignments, dependent on the chosen topology (refer to the CN5000 Topologies and Routing Guide), which must be shared between QoS vFabrics. SLs can share the same VL, separated by QoS, so traffic will not interact and remain independent.
QoS Operation
Virtual Lanes (VLs) permit multiple logical flows over a single physical link. Each physical link has a number of VLs. Each class of service has a Service Level (SL). The local route header of the packets carries the SL, which identifies the different flows within the subnets. The amount of resources allocated to the VL is based on the bandwidth configured for the vFabric containing the SL. The Subnet Manager programs the SL-to-VL mappings and VL Arbitration tables to achieve the QoS policies.
Applications can query for path records by Service ID to obtain path records associated with the given application. These path records contain the SL associated with the traffic class/QoS vFabric. In turn, this SL is used for packets within this class of traffic.