If you have 2 real CPUs, they are real CPU 0 and real CPU 1. Real CPU 0 will never be dedicated to a guest. If a guest logs on and has a dedicated virtual CPU and a real CPU is free that is not real CPU 0, A real CPU will be assigned to that virtual CPU. If a real CPU is not available then the virtual CPU will be one of the CPU that can be dispatched on any available CPU.
The effect of having the statement CPU 01 DEDICATE in every guest with only 2 real CPUs is - The first guest to logon will have real CPU 01 assigned to the guest as virtual CPU 01. That guest will be the only one using real CPU 1 until it logs off. All other guests that logon while real CPU 1 is assigned will be placed in the dispatching queue. Those guest will be dispatched on real CPU 0 as it is the only one available. So we have the first guest using real CPU 1 and all other guests sharing real CPU 0. If the first guest logs off, that will free real CPU 1 and VM will start dispatching guests on it. Then we will have all the guest sharing both real CPU 0 and real CPU 1. However if another guest logs on it will then be assigned CPU 1 and VM will stop dispatching the other guests on it. Unless you only need 1 real CPU to get your work done, you will see strange performance problems. You will have one guest running well and all the other guests doing poorly. But when the guest that is running well logs off everyone else will start running well until a new guest logs on and then the other guests will go back to poor performance. RPN01 wrote:
Someone else had said something about only the first guest logging in being dedicated, but I don't think that is how it would work; If that were true, guest one would get CPU 01, guest 2 would get CPU 00, and everyone else would starve for CPU. Now... Having said that, if someone from IBM or elsewhere understands the CPU DEDICATE option differently, please feel free to educate me; we'll all learn from it.
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