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

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partiti<strong>on</strong> with 0.50 processing units was assigned two virtual processors and<br />

processing resources were available, the partiti<strong>on</strong> could use an additi<strong>on</strong>al 1.50<br />

processing units.<br />

The minimum number of processing units you can have for each virtual<br />

processor depends <strong>on</strong> the server model. The maximum number of processing<br />

units that you can have for each virtual processor is always 1.00. This means that<br />

a logical partiti<strong>on</strong> cannot use more processing units than the number of virtual<br />

processors that it is assigned, even if the logical partiti<strong>on</strong> is uncapped.<br />

Additi<strong>on</strong>ally, the number of processing units cannot exceed the Total Managed<br />

system processing units.<br />

Virtual processor folding<br />

Starting with maintenance level 3, AIX 5L V5.3 provides an improved<br />

management of virtual processors. This feature enhances the utilizati<strong>on</strong> of a<br />

shared processor pool by minimizing the use of virtual processors that are idle<br />

most of the time. The important benefit of this feature is improved processor<br />

affinity, when there is a large number of largely idle shared processor partiti<strong>on</strong>s,<br />

resulting in effective use of processor cycles. It increases the average virtual<br />

processor dispatch cycle, resulting in better cache utilizati<strong>on</strong> and reduced<br />

Hypervisor workload.<br />

The following are the functi<strong>on</strong>s of the virtual processor folding feature:<br />

► Idle virtual processors are not dynamically removed from the partiti<strong>on</strong>. They<br />

are put to sleep or disabled, and <strong>on</strong>ly awoken when more work arrives.<br />

► There is no benefit from this feature when partiti<strong>on</strong>s are busy.<br />

► If the feature is turned off, all virtual processors defined for the partiti<strong>on</strong> are<br />

dispatched to physical processors.<br />

► Virtual processors having attachments, such as bindprocessor or rset<br />

command attachments, are not excluded from being disabled.<br />

► The feature can be turned off or <strong>on</strong>. The default is <strong>on</strong>.<br />

When a virtual processor is disabled, threads are not scheduled to run <strong>on</strong> it<br />

unless a thread is bound to that CPU.<br />

Note: In a shared partiti<strong>on</strong>, there is <strong>on</strong>ly <strong>on</strong>e affinity node, hence <strong>on</strong>ly <strong>on</strong>e<br />

node global run queue.<br />

The tunable parameter for this feature is vpm_xvcpus and the default value is 0,<br />

which signifies the functi<strong>on</strong> is <strong>on</strong>. Use the schedo command to change the<br />

tunable parameter.<br />

36 <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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