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Question about ESXi cpu scheduler

HI Everybody.
Question about the esx cpu scheduler. Is the guest os schedules something to run on 4 cores then esxi will run it on 4 cores, right? Or is there a situation where the guest can schedule 4 cores and esx would actually run it on less than 4?


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One Comment

  1. The host doesn’t allocate cores to virtual machines in the way that I believe you may be thinking.

    Basically, if you have a 1:1 CPU Core/vCPU config, then yes. You’ll essentially have a physical core per vCPU (not considering hyper-threading). But in reality the scheduler is just using each time slot to process your vCPU requests at the same time. You’re never directly communicating with the CPU core. If you have a 1:2 CPU Core/vCPU configuration, the scheduler would just have to make the vCPUs wait to communicate with a CPU core.

    I’d recommend doing some reading on the topic, as there is a reason white-papers and a load of documentation exists on the subject. This page goes into it slightly more than I have: https://kloudkonnect.wordpress.com/2019/08/23/understanding-esxi-cpu-scheduling/

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