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Advanced POWER Virtualization on IBM System p5 - Previous ...

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The benefit of SMT is greatest where there are numerous c<strong>on</strong>currently executing<br />

threads, as is typical in commercial envir<strong>on</strong>ments, for example, for a Web server<br />

or database server. Data-intensive, memory bound, or single-threaded high<br />

performance computing workloads will generally perform better with ST.<br />

2.5.2 SMT and AIX 5L<br />

The AIX 5L operating system scheduler dispatches executi<strong>on</strong> threads to logical<br />

processors. Dedicated and virtual processor have <strong>on</strong>e or two logical processors<br />

depending whether SMT is enabled or not. With SMT enabled, both logical<br />

processors are always in the same partiti<strong>on</strong>. Figure 2-6 shows the relati<strong>on</strong>ship<br />

between physical, dedicated, and logical processors for dedicated and<br />

shared-processor partiti<strong>on</strong>s. It is possible to have some shared-processor<br />

partiti<strong>on</strong>s with SMT enabled and others with SMT disabled at the same time.<br />

Dedicated-processor partiti<strong>on</strong> SMT=off<br />

Shared-processor partiti<strong>on</strong> SMT=<strong>on</strong><br />

Logical<br />

CPU<br />

Logical<br />

CPU<br />

Logical<br />

CPU<br />

Logical<br />

CPU<br />

Logical<br />

CPU<br />

Logical<br />

CPU<br />

Logical<br />

CPU<br />

Logical<br />

CPU<br />

Physical<br />

Processor<br />

Physical<br />

Processor<br />

Virtual<br />

Processor<br />

Virtual<br />

Processor<br />

Virtual<br />

Processor<br />

Shared processor pool<br />

Physical<br />

Processor<br />

Physical<br />

Processor<br />

Figure 2-6 Physical, virtual, and logical processors<br />

SMT c<strong>on</strong>trol in AIX 5L<br />

SMT enablement is c<strong>on</strong>trolled by the AIX 5L smtctl command or with the system<br />

management interface tool (SMIT). SMT can be enabled or disabled dynamically<br />

<strong>on</strong> a logical partiti<strong>on</strong> or for the next operating system reboot.<br />

46 <str<strong>on</strong>g>Advanced</str<strong>on</strong>g> <str<strong>on</strong>g>POWER</str<strong>on</strong>g> <str<strong>on</strong>g>Virtualizati<strong>on</strong></str<strong>on</strong>g> <strong>on</strong> <strong>IBM</strong> <strong>System</strong> <strong>p5</strong>

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