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IBM's AIX has a "virtual context switch" column in lparstat but neither IBM's redbooks nor google searches will tell me what exactly a virtual context switch is and how its different from a regular context switch. All my searches yield what a regular context switch is as thats a more well defined and universal OS concept.

So, what is a "virtual context switch" in the context of a SPLPAR configuration with a shared processor pool and virtual processors?

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A virtual context switch is when one virtual processor yields resources to another virtual processor.

http://www.ibm.com/developerworks/aix/library/au-syspvirtualization/index.html#N101F8

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  • So does that mean that when a VP has no more work to do a virtual context switch is recorded when it gives up its remaining time to any other VPs that need it? I'm trying to diagnose what seeing 500,000 (yes half a million) virtual context switches on a badly behaving machine means exactly.
    – bot403
    Jun 2, 2011 at 0:29
  • No, I suppose I'm overthinking it. Its exactly like a regular context switch but on a virtual processor. A process running on a VP hasn't completed but the hypervisor is deciding to evict it for another process so must save the state of the first process. Right?
    – bot403
    Jun 2, 2011 at 1:18

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