Tuning the global resource serialization ring

If a global resource serialization ring complex is running without disruption, slowdowns are usually caused by an improperly tuned ring. Delay of the RSA message can become pronounced on larger complexes, delaying the initiation of new workload. To "speed up the ring", the installation can take one, two, or all of the following actions.

• Speed up the RSA.

  The speed of the RSA message is dependent on the RESMIL values specified in GRSCNFxx or the SETGRS RESMIL= command. Determine the RESMIL values used by each of the systems in the complex. To improve ENQ/DEQ response time, decrease the RESMIL value used on all the systems in the complex. You can use the ROUTE *ALL command to effect the change on all systems at one time. Try using a RESMIL of 1 or 2. If this does not meet your performance goals, try a RESMIL of 0.

  There is also a RESMIL setting of OFF. Use this setting carefully, as all of the other RESMIL values are tuned automatically by the complex. If the ring is lightly loaded, global resource serialization will tune the RESMIL value up one millisecond each time an empty RSA makes a trip around the sysplex until RESMIL reaches the specified value plus 5 (RESMIL=1 will tune between 1 and 6 milliseconds). When the ring becomes loaded, RESMIL returns to the specified value. When an installation specifies RESMIL=OFF, the RSA will be sent immediately after receipt and processing by each system, without tuning. This might adversely impact processor performance.

• Use Ring Acceleration.

  Ring acceleration improves performance by reducing the number of systems that must see an ENQ before the issuing system might grant ownership of the resource. This reduces the time between a system receiving the RSA and granting a resource request (but does not decrease the system's wait time for the RSA). There are possible integrity concerns introduced by the use of ring acceleration, but the opportunity for such failures is small. By specifying ACCELSYS(2), an installation can reduce the overall response time for an ENQ/DEQ request. See Ring acceleration (ACCELSYS) for more information.

• Use Star Mode.

  By far, a global resource serialization star complex outperforms any ring complex, usually by orders of magnitude, with fewer recovery and operational concerns. IBM® guidelines suggest that all installations migrate to a star complex whenever possible.