smp bug in kvm-69

smp bug in kvm-69

[Farkas Levente]

hi,
we just noticed that while we run a guest with 4vcpu (the host has 4 core):
-----------------------------------------
  3278 ?        Sl   2138:49 /usr/bin/qemu-kvm -M pc -m 2048 -smp 4
-monitor pty -boot c -hda /dev/VolGroup00/centos-i386-root -hdb
/dev/VolGroup00/centos-i386-swap -hdc /dev/md2 -net
nic,macaddr=00:16:3e:58:66:7b,vlan=0 -net
tap,fd=11,script=,vlan=0,ifname=vnet0 -usb -usbdevice tablet -vnc
127.0.0.1:0
-----------------------------------------
the guest only see 3 cpu?:
-----------------------------------------
# cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 2
model name      : QEMU Virtual CPU version 0.9.1
stepping        : 3
cpu MHz         : 2399.968
cache size      : 2048 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu de pse tsc msr pae mce cx8 apic mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 syscall nx lm pni
bogomips        : 4806.74

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 6
model           : 2
model name      : QEMU Virtual CPU version 0.9.1
stepping        : 3
cpu MHz         : 2399.968
cache size      : 2048 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu de pse tsc msr pae mce cx8 apic mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 syscall nx lm pni
bogomips        : 4800.27

processor       : 2
vendor_id       : GenuineIntel
cpu family      : 6
model           : 2
model name      : QEMU Virtual CPU version 0.9.1
stepping        : 3
cpu MHz         : 2399.968
cache size      : 2048 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu de pse tsc msr pae mce cx8 apic mtrr pge mca cmov
pat pse36 clflush mmx fxsr sse sse2 syscall nx lm pni
bogomips        : 4797.91
-----------------------------------------


-- 
   Levente                               "Si vis pacem para bellum!"

Re: smp bug in kvm-69

[Avi Kivity]

Farkas Levente wrote:
> hi,
> we just noticed that while we run a guest with 4vcpu (the host has 4 
> core):
> -----------------------------------------
>  3278 ?        Sl   2138:49 /usr/bin/qemu-kvm -M pc -m 2048 -smp 4
> -monitor pty -boot c -hda /dev/VolGroup00/centos-i386-root -hdb
> /dev/VolGroup00/centos-i386-swap -hdc /dev/md2 -net
> nic,macaddr=00:16:3e:58:66:7b,vlan=0 -net
> tap,fd=11,script=,vlan=0,ifname=vnet0 -usb -usbdevice tablet -vnc
> 127.0.0.1:0
> -----------------------------------------
> the guest only see 3 cpu?:
> -----------------------------------------


Does this happen every time?  Is the host loaded when you start the 
guest with some other task?

It may be that there is some guest timeout during startup which causes 
the cpu to go missing.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

Re: smp bug in kvm-69

[Farkas Levente]

Avi Kivity wrote:
> Farkas Levente wrote:
>> hi,
>> we just noticed that while we run a guest with 4vcpu (the host has 4 
>> core):
>> -----------------------------------------
>>  3278 ?        Sl   2138:49 /usr/bin/qemu-kvm -M pc -m 2048 -smp 4
>> -monitor pty -boot c -hda /dev/VolGroup00/centos-i386-root -hdb
>> /dev/VolGroup00/centos-i386-swap -hdc /dev/md2 -net
>> nic,macaddr=00:16:3e:58:66:7b,vlan=0 -net
>> tap,fd=11,script=,vlan=0,ifname=vnet0 -usb -usbdevice tablet -vnc
>> 127.0.0.1:0
>> -----------------------------------------
>> the guest only see 3 cpu?:
>> -----------------------------------------
> 
> 
> Does this happen every time?  Is the host loaded when you start the 
> guest with some other task?

no just sometimes, sometimes nont

> It may be that there is some guest timeout during startup which causes 
> the cpu to go missing.
> 

you knows:-)

-- 
   Levente                               "Si vis pacem para bellum!"