Red Hat and related distro's (like CentOS) use 1000 timer interrupts per second, per CPU core or thread (this is called the "HZ value" inside the kernel). Because this causes a lot of extra work in case of virtualization, and caused (past tense since RHEL 5.4!) problems with timekeeping, the " divider " kernel parameter has been introduced. For example, by booting with "divider=10", the kernel uses 100 timer interrupts instead of 1000, and "divider=25" means 40 timer interrupts per second. I did a little test today to see what difference that makes when running CentOS5.4 on vSphere. Tests were done with the current 2.6.18-164.11.1.el5 x86_64 kernel in a single vCPU VM. These are the results from my test environment: standard settings: HZ=1000: 60 MHz cycles used when idle. divider=2: HZ=500: 36 MHz cycles used when idle. divider=5: HZ=200: 25 MHz cycles used when idle. divider=10: HZ=100: 20 MHz cycles used when idle. divider=25: HZ=40: a...
plenty of grains to pick