Re: why guests show "Clocksource tsc unstable" on bootup?

[Avi Kivity <avi@redhat.com>]

Tomasz Chmielewski wrote:
> Avi Kivity schrieb:
>> Tomasz Chmielewski wrote:
>>> Why do my guests show "Clocksource tsc unstable" on bootup?
>>>
>>
>> Linux expects the tsc to be monotonic and to have a 1:1 
>> correspondence with real time, which isn't easy to achieve with 
>> virtualization.
>
> But the clocksource is kvm-clock, so why does the guest probe tsc at all?
>

Good question.  I don't know what the answer is.  Maybe the scheduler 
uses tsc for its internal clock.

>
> I pasted a part of /proc/cpuinfo below.
> I saw these with kvm-83 and kvm-84 (with cpufreq disabled, as it 
> perhaps can matter).
>
> processor       : 3
> vendor_id       : AuthenticAMD
> cpu family      : 15
> model           : 65
> model name      : Dual-Core AMD Opteron(tm) Processor 2212
> stepping        : 2
> cpu MHz         : 2000.000
> cache size      : 1024 KB
> physical id     : 1
> siblings        : 2
> core id         : 1
> cpu cores       : 2
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 1
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge 
> mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext 
> fxsr_opt rdtscp lm 3dnowext 3dnow rep_good pni cx16 lahf_lm cmp_legacy 
> svm extapic cr8_legacy
> bogomips        : 3993.03
> TLB size        : 1024 4K pages
> clflush size    : 64
> cache_alignment : 64
> address sizes   : 40 bits physical, 48 bits virtual
> power management: ts fid vid ttp tm stc
>

This cpu indeed has unstable tsc, but disabling cpufreq should have 
fixed it.

Maybe we need to disable C-states as well?


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