Prioritizing outbound OSA-Express data using the Workload Manager service class

The z/OS® Workload Manager (WLM) provides a priority associated with each unit of work that runs a TCP/IP socket API to send data. The priority provided by WLM is related to the WLM service class associated with the unit of work. The unit of work can derive its priority from the service class associated with the address space in which it is running or from the service class associated with the enclave to which it belongs. The priorities provided by WLM, from highest priority to lowest priority, are as follows:

  • System-defined service class (SYSTEM), used for system address spaces
  • System-defined service class (SYSSTC), used for high-priority started tasks
  • User-defined service classes with importance level 1
  • User-defined service classes with importance level 2
  • User-defined service classes with importance level 3
  • User-defined service classes with importance level 4
  • User-defined service classes with importance level 5
  • User-defined service classes associated with a discretionary goal

For more information about WLM and the WLM service classes, see z/OS MVS Planning: Workload Management and z/OS MVS Programming: Workload Management Services.

z/OS Communications Server supports four priority values for outbound QDIO traffic, 1 through 4, with 1 being the highest priority. Priorities with lower numbers are given preferential treatment by the QDIO device driver and the OSA-Express® feature.

You can specify the QDIO priority value to be used on the SetSubnetPrioTosMask statement in a Quality of Service (QoS) policy, which provides one way to influence the QDIO traffic priority that is used for outbound packets. The SetSubnetPrioTosMask statement maps the IPv4 type of service (ToS) byte or IPv6 traffic class to these four QDIO traffic priorities. For more information about the SetSubnetPrioTosMask statement, see z/OS Communications Server: IP Configuration Reference.

Another way to influence the QDIO traffic priority is to use the WLMPRIORITYQ parameter on the GLOBALCONFIG profile statement. The WLMPRIORITYQ parameter automatically extends the preferential treatment of the most important workloads for a business through the QDIO device driver all the way to the LAN. When the WLMPRIORITYQ parameter is specified and a packet with a ToS or traffic class value 0 is sent over an OSA-Express feature in QDIO mode, Communications Server sets the OSA-Express write priority of the packet based on the priority value provided by the WLM service class. In addition, the WLMPRIORITYQ parameter can be used to influence the QDIO traffic priority of forwarded packets with a ToS or traffic class value 0.

For more information about the GLOBALCONFIG statement, see z/OS Communications Server: IP Configuration Reference.

Restrictions:
  • Prioritization using the WLM service class is effective only when enabled and when the ToS or traffic class value is 0.
  • Prioritization using the WLM service class is ineffective for interfaces other than OSA-Express features in QDIO mode.
  • Prioritization of forwarded packets is ineffective unless DATAGRAMFWD is specified on the IPCONFIG statement, the IPCONFIG6 statement, or both statements.
  • The WLMPRIORITYQ setting for forwarded packets has no effect on accelerated packets. To set the write priority for accelerated packets, use QDIOPRIORITY on the IQDIOROUTING parameter or the QDIOACCELERATOR parameter on the IPCONFIG profile statement. For more information about the IPCONFIG statement, see z/OS Communications Server: IP Configuration Reference.