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The supported operating systems are listed in Table 7-3 on page 214 and Table 7-4 on page 216. 

An operating system that uses SMT controls each core and is responsible for maximizing their throughput and meeting workload goals with the smallest number of cores. In z/OS, HiperDispatch cache optimization should be considered when you must choose the two threads to be dispatched in the same processor. 

HiperDispatch attempts to dispatch guest virtual CPUs on the same logical processor on which they ran. PR/SM attempts to dispatch a vertical low logical processor in the same physical processor. If that process is not possible, it attempts to dispatch it in the same node, or then the same CPC drawer where it was dispatched before to maximize cache reuse. 

From the perspective of an application, SMT is transparent and no changes are required in the application for it to run in an SMT environment, as shown in Figure 7-1. 

<img src='content_image/1004500.jpg'>

## z/OS 

The following APARs must be applied to z/OS V2R1 to use SMT: 

GLYPH<SM590000> OA43366 (BCP) 

GLYPH<SM590000> OA43622 (WLM) 

GLYPH<SM590000> OA44439 (XCF) 

The use of SMT on z/OS V2R1 requires enabling HiperDispatch, and defining the processor view ( PROCVIEW ) control statement in the LOADxx parmlib member and the MT_ZIIP_MODE parameter in the IEAOPTxx parmlib member. 

The PROCVIEW  statement is defined for the life of IPL, and can have the following values: 

GLYPH<SM590000> CORE : This value specifies that z/OS should configure a processor view of core, in which a core can include one or more threads. The number of threads is limited by z14 ZR1 to two threads. If the underlying hardware does not support SMT, a core is limited to one thread. 

GLYPH<SM590000> CPU : This value is the default. It specifies that z/OS should configure a traditional processor view of CPU and not use SMT. 

GLYPH<SM590000> CORE,CPU_OK : This value specifies that z/OS should configure a processor view of core (as with the CORE  value) but the CPU parameter is accepted as an alias for applicable commands. 

When PROCVIEW CORE  or CORE,CPU_OK  are specified in z/OS that is running in z14 ZR1, HiperDispatch is forced to run as enabled, and you cannot disable HiperDispatch. The PROCVIEW  statement cannot be changed dynamically; therefore, you must run an IPL after changing it to make the new setting effective. 

