setting CPU entitlement for AIX 6.1

Hi I would like to understand LPAR entitlement's better.

If I have a system that is running AIX 6.1 with an uncapped LPAR, what do I lose by setting the entitlement low? Meaning theoretically if I need more CPU power and more CPU's are available then I should see additional Lpars unfold and get more power, does this unfolding开发者_开发问答 cause a system performance hit?

Is there a formula for setting CPU entitlement for AIX 6.1?

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Another downside to undersizing your entitlement has to do with Power's NUMA architecture and allocation of VCPU threads to real processors. If you are constantly overrunning your entitlement, allocation of these threads to CPUs won't be as optimal when it comes to having the application code/data dispatched to a CPU with that data close by, preferably in L1 or L2 cache.

In other words, the system does a better job of reducing remote memory transfers to support a thread on a CPU, when you're not overrunning your entitlement, boosting performance.

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I know understand the issue. Its more than just requesting extra resources

any capacity used beyond an LPAR's entitled capacity isn’t guaranteed (as it might be some other LPAR's entitlement)

Meaning that you can be forced down to 100% use when you really need more. Lesson: Don't get your entitlement wrong.

http://www.ibmsystemsmag.com/aix/Micro-Partitioning_on_AIX/32920p1.aspx