Workload, capacity, and performance 45Draft Document for Review October 18, 2004 5486wrkperf.fm Processor CPW: Represents maximum relative performance runningcommercial processing workloads for a processor configuration. Use thisvalue to compare relative performance between models with the same ordifferent number of processors. 5250 CPW: Represents the relative performance available to perform 5250OLTP (interactive) workloads.Simultaneous multithreading explainedAlthough an operating system gives the impression that it is concurrentlyexecuting a large number of tasks, each processor in a symmetric multiprocessor(SMP) traditionally executes a single task’s instruction stream at any moment.The QPRCMLTTSK system value controls whether to enable the individual SMPprocessors to concurrently execute multiple instruction streams. Each instructionstream belongs to separate tasks or threads. When enabled, each individualprocessor concurrently executes multiple tasks at the same time. The effect of itsuse will likely increase the performance capacity of a system or improve theresponsiveness of a multithreaded application.Running multiple instruction streams at the same time does not improve theperformance of any given task. Since this is the case with any performancerecommendations, results vary in different environments.The way that multithreading is done depends on the hardware model, andtherefore, the performance capacity gains vary. IBM Eserver i5 Models 520,550, 570, and 595 support this approach through a concept called simultaneousmultithreading (SMT). There are several distinct differences between differenttypes of multithreading implemented in the industry. You may find articlesdiscussing Intel’s Hyper-Threading, Superthreading, and other multitaskingtechniques from several sources.Older iSeries processors use an approach called hardware multithreading(HMT). In the hardware multithreading approach, the hardware automaticallyswitches between the tasks on any long processing delay event, for example, acache miss. Some models do not support any form of multithreading, whichmeans the QPRCMLTTSK system value has no performance effect. Because theQPRCMLTTSK system value enables the parallel use of shared processorresources, the performance gains depend highly on the application and theImportant: Limited 5250 CPW is always available for a system administratorto use 5250 display device I/O to manage various aspects of the server.Multiple administrative jobs quickly exceed this limited 5250 capacity.
