100% cpu load on host with 1000hz guest kernels

[Niki Waibel]

yes, the manual says:

11.3 Linux guests
11.3.1 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.

but i'd like to request an enhancement to fix this.

sure, using a 100hz guest kernel helps, reducing the load on the host. but running 10 100hz guest kernels will give the same problem.

further, running 1000hz kernels on other virtualisation sw works just smoothly. this means, with some effort, it is possible to fix this issue.

[Sander van Leeuwen]

Did you try running 10 100hz guests? I don't see any reason why that should cause a problem.

Also running a 1000 hz guest should be fine if the host timer resolution matches.

[Niki Waibel]

yes, 10 100hz guests cause the host system to be idle around 60%. the 10 VirtualBox processes use between 1 and 10%cpu, and spread around the 2 cores of the host.

1 1000Hz guest cause the host system to be idle around 55%. the VirtualBox process use around 43% cpu.

100hz guests: dsl-4.4.10, linux-2.4.31

1000hz guest: centos-5.3, linux-2.6.18-128.1.10.el5.centos.plus

host: CONFIG_NO_HZ=y CONFIG_HZ_300=y CONFIG_HZ=300 linux-2.6.29.1, 2x Intel(R) Core(TM)2 Duo CPU T7300 @ 2.00GHz scaling_governor: performance

the only solution right now is to use an old 100hz centos vm-kernel, distributed on ​http://people.centos.org/tru/kernel-vm

[Niki Waibel]

same situation with 3.0.2.

[Niki Waibel]

same for 3.0.4

[Technologov]

The problem still exists for VBox 3.2.6, and I don't know if this is 'fixable' or not. Especially true for SMP guests, where guest's keyboard makes several presses on each real (host keyboard's) key press (RHEL5 guest with 16 vCPUs).

My recommendation: Boot Linux guests with "divider=10". This will slow down their clocks from 1000Hz to 100Hz.

-Technologov

[Technologov]

A possible idea: VBoxLinuxAdditions could detect the high frequency timer in (Red Hat) Linux guests, and add "divider=10" to the GRUB config file.

This looks like a reasonable middle ground, where this solution will work for 90%+ of the users, without requiring them deep Linux skills and kernel recompilations.

-Technologov