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, as well as kernels of related Linux distributions, such as CentOS and Oracle Linux, support a kernel parameter divider=N. Hence, such kernels support a lower timer frequency without recompilation. We suggest you add the kernel parameter divider=10 to select a guest kernel timer frequency of 100Hz.
VirtualBox ... the above section from the documentation would tend to suggest this may be connected to something I'm seeing, so my question is "what timer frequency is the COS7 kernel compiled to use? - and is the divider parameter implemented in the COS kernel (presumably 'yes' given it originates from CentOS?)
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Accepted AnswerRichard GeorgeOffline
Accepted AnswerNick HowittOfflineThis is old (EL5) but they recommend not to use "divider". It appears this is just a boot parameter which you can supply at boot time or update your grub.cfg. Since 7.7 the kernel is Centos's untouched. I've no idea how to find out what is compiled in but I'm sure, with a load of googling, I could find it.