I'm running a FreeBSD 9.0 setup as a virtual machine in a KVM setup. In previous versions of FreeBSD it was common to force the
kern.hz setting to a lower value so that the virtual machine does not keep the host busy because it's handling timer interrupts without having any work to do - the FreeBSD Handbook explains:
The most important step is to reduce the kern.hz tunable to reduce the CPU utilization of FreeBSD under the Parallels environment. This is accomplished by adding the following line to
Without this setting, an idle FreeBSD Parallels guest OS will use roughly 15% of the CPU of a single processor iMac®. After this change the usage will be closer to a mere 5%.
However, in FreeBSD 9, the "dynamic tick mode" (aka "tickless mode") is the default, controlled by the
kern.eventtimer.periodic setting which defaults to
0 (read: tickless mode).
This makes me wonder - does the tip of lowering
kern.hz still have any relevance for making FreeBSD 9 play nicely in a virtual machine setup?