[Qemu-discuss] FreeBSD 9.1/amd64 guest: "calcru: runtime went backwards"

[Peter Kieser]

Hello,

I am experiencing an issue with a FreeBSD 9.1/amd64 guest which has 2 
vCPU running under qemu 1.4.2 built from source (it also happens in 
previous releases) with KVM enabled where I receive the following 
messages on the guest (the time is going backwards?):

Jun 22 12:02:02 azazel kernel: calcru: runtime went backwards from 503 
usec to 318 usec for pid 0 (kernel)
Jun 22 12:02:02 azazel kernel: calcru: runtime went backwards from 31 
usec to 19 usec for pid 0 (kernel)
Jun 22 12:02:02 azazel kernel: calcru: runtime went backwards from 
30239519 usec to 19110702 usec for pid 0 (kernel)

I have tried switching the time source in the guest to use TSC, ACPI, 
and PIT (the default is HPET, which I believe is emulated under qemu?) - 
after a few days regardless of the time source specified in the guest, I 
see these error messages again in the kernel logs. Additionally, I have 
tried the same time sources list above but using "-rtc 
base=localtime,driftfix=slew -no-hpet" option for qemu but the issue 
persists. I have also tried enabling ticks in the FreeBSD kernel, as 
they are disabled in the 9.1 release - with no result (in fact, time is 
lost faster: at 4s an hour.)

The host system is running Ubuntu 12.04.2 (3.2.0-43-generic kernel) with 
an Intel i5-3570S which has the constant_tsc CPU flag present - and CPU 
power management is also disabled.

Is there a way to fix the issue, or a known bug? I do not have a similar 
issue on my Linux or Windows guests.

Thank you,

-Peter Kieser <address@hidden>

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