[Qemu-devel] linux verify_pmtmr_rate() issue

[Matthew Kent <mkent@magoazul.com>]

Issue here that's beyond my skill set to resolve:

I've been starting multiple linux 2.6.23-rc3 x86 guests up in parallel
with qemu/kvm and noticed pm-timer is being disabled in some of them
with

PM-Timer running at invalid rate: 126% of normal - aborting.

in dmesg when I start about 6 at a time. Unfortunately without the timer
a tickless kernel in my guests is disabled. 

I also replicated the issue by starting a single vm when the host system
was busy enough.

After some amateurish debugging added to verify_pmtmr_rate() in the
kernel acpi_pm driver and get_pmtmr() in qemu acpi I can indeed see it
returning just slowly enough to throw off the sanity check. 

[   10.264772] DEBUG: PM-Timer running value1: 2925874 value2: 3058371
expected_rate: 107385 delta: 132497 count: 2269
[   10.270766] PM-Timer running at invalid rate: 123% of normal -
aborting.

For now I've just disabled verify_pmtmr_rate() in the kernel for my
guests and they seem to be keeping time just fine. 

Not sure if a patch for the linux kernel making the sanity check
optional with a kernel parameter would make sense or there's something
else that can be done at the qemu level.

Thanks.
-- 
Matthew Kent <mkent@magoazul.com>
http://magoazul.com