I am using VirtualBox on a Macbook Pro running Yosemite.
My linux guests sometimes consume 100% of the host CPU (viewed in Activity Monitor) even though the guest is idle.
Why is the host CPU utilization so high and how can this be fixed?
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From the VirtualBox manual:
12.4.1. Linux guests may cause a high CPU load
Some Linux guests may cause a high CPU load even if the guest system appears to be idle. This can be caused by a high timer frequency of the guest kernel. Some Linux distributions, for example Fedora, ship a Linux kernel configured for a timer frequency of 1000Hz. We recommend to recompile the guest kernel and to select a timer frequency of 100Hz.
Linux kernels shipped with Red Hat Enterprise Linux (RHEL) as of release 4.7 and 5.1 as well as kernels of related Linux distributions (for instance CentOS and Oracle Linux) support a kernel parameter divider=N. Hence, such kernels support a lower timer frequency without recompilation. We suggest to add the kernel parameter divider=10 to select a guest kernel timer frequency of 100Hz.