Re: Houston, we have May 15, 1953 (says guest when host uses cpufreq, and dies)

Tomasz Chmielewski
2009-02-18T18:53:18Z

Marcelo Tosatti schrieb:
> On Wed, Feb 18, 2009 at 03:51:22PM +0100, Tomasz Chmielewski wrote:
>> Is using cpufreq (i.e. with ondemand governor) on KVM host safe for guests?
>>
>> I enabled cpufreq on the host, it scaled down the host CPU (Dual-Core
>> AMD Opteron(tm) Processor 2212) to 1 GHz from 2 GHz.
>>
>> Guest (using 1 CPU) was still showing that it has a 2 GHz CPU in
>> /proc/cpuinfo (I guess this value is read only once, when booting).
>>
>> After about 2 hours I started "date" on the guest - it showed that it's
>> year *1953*, after which I couldn't start any other command (the guest
>> was technically alive - SSH connection to it didn't die - but I couldn't
>> do anything).
>>
>> # date
>> Wed Feb 18 13:07:17 CET 2009
>>
>> [let's wait ~2 hours]
>>
>>
>> # date
>> Fri May 15 10:13:14 CET 1953
>> # date
>> ^C^Z
>> [could not interrupt]
>>
>>
>> Is it expected behaviour? Is it correct behaviour?
>
> Whats the output of /proc/cpuinfo on the host? Does it contain the
> constant_tsc flag?

It doesn't contain this flag.
/proc/cpuinfo output - below.

> Whats the output of
> /sys/devices/system/clocksource/clocksource0/current_clocksource
> on the guest?

# cat /sys/devices/system/clocksource/clocksource0/*
hpet acpi_pm jiffies tsc <- available
hpet <- current

# cat /proc/cpuinfo
processor : 0
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 : 0
siblings : 2
core id : 0
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 : 3993.20
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

processor : 1
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 : 0
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 : 3993.20
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

processor : 2
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 : 0
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 : 3993.20
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

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 : 3993.20
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