unstable clocksource when running Xen inside virtualbox

[Sven]

I'm using virtualbox to test Xen 4.1.1 + Linux 3.0 dom0. By default, the Xen hypervisor tries to use the ACPI PM timer as a clocksource. It seems to be unstable and Xen complains about the timer wrapping around unexpectedly. A HPET doesn't seems to be available. The only clocksource that seems to be stable is clocksource=pit. (The dom0 kernel has clocksource=xen)

Note, that with ACPI PM timer as a clocksource, dom0 becomes and unstable and AHCI various errors pop up during HDD I/O.

This is easily reproducable here (it doesn't happen every time, but it happens very often) with VirtualBox 4.1, 64Bit Core i5 Linux host, dual core, hyperthreading. The guest is configured as OS=Other/Unknown, 4 CPUs, VT-x and Nested Paging enabled.

[Frank Mehnert]

Is this problem still reproducible with VBox 4.1.8? There were some fixes related to the ACPI timer some VBox releases ago. The ACPI timer should be definitely stable now.

[Sven]

I removed clocksource=pit, and xen seems to use the ACPI time as a clocksource now. However, ahci errors popped up again in 2 of 3 boots.

I have been using the virtual machine with clocksource=pit very reliably.

[Sven]

The problems seems to have gone for now. I'm not using kernel 3.7.2 and virtualbox 4.2.6 on the host and inside the guest it's xen 4.2 and dom0 kernel 3.7.2.