Improve performance with QDIO Accelerator

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The QDIO Accelerator function can boost performance of IPv4 traffic forwarded over OSA-Express QDIO and HiperSockets interfaces including sysplex distributor traffic which is routed to a target stack. The optimized packet forwarding provided by QDIO Accelerator improves latency and reduces CPU consumption.

The function applies to traffic which arrives inbound over an OSA-Express QDIO or HiperSockets interface and is forwarded outbound over OSA-Express QDIO or HiperSockets. With QDIO Accelerator, the first time such a packet is forwarded using a given route in the stack routing table, the z/OS stack creates a QDIO Accelerator route. Subsequent eligible packets which would normally be forwarded by the stack on this route instead get processed at the DLC layer without having to traverse the forwarding stack. This provides a much more efficient path for that traffic. 

QDIO Accelerator can be especially valuable for sysplex distributor traffic being forwarded to a target stack when you do at least one of the following:

• use HiperSockets to provide dynamic XCF connectivity between stacks on the same CPC
• use VIPAROUTE to route packets to a target stack over an OSA-Express QDIO interface 

To enable the QDIO Accelerator function, specify QDIOACCELERATOR on the IPCONFIG statement in the TCP/IP profile of any stack which will perform IP forwarding or which is serving as a sysplex distributor stack. You can enable VIPAROUTE to a specific target stack by using the VIPAROUTE statement in the VIPADYNAMIC block. With VIPAROUTE, the stack forwards packets from the distributor stack to a target stack using a route from the stack routing table rather than using the dynamic XCF connectivity. 

To display the QDIO Accelerator routes, use the Netstat ROUTE/-r report option with the QDIOACCEL modifier. You can use the Netstat VCRT/-V report with the DETAIL modifier to see which sysplex distributor connections are eligible for acceleration. 

With VTAM tuning statistics, you can display information such as the number of packets and bytes accelerated for each interface. Because the accelerated packets do not traverse the forwarding stack, these packets are not included in a packet trace on that stack. However, these are included in an OSA-Express Network Traffic Analyzer (OSAENTA) trace.

Beginning with z/OS CS V2R1, QDIO Accelerator can co-exist with IP security. IP forwarded packets can be accelerated as long as all routed traffic is permitted by your IP filter policy and is not subject to logging. Sysplex distributor traffic is always eligible for acceleration using QDIO Accelerator because these packets are subject to IP filtering at the target stack rather than the distributor stack.