Re: [Xen-users] domain reboots after migrating between hosts

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> I have two Xen hosts, A and B, both running Xen 3.0.4.
>
> When I migrate a guest domains from A to B, they reboot themself as soon
> as the migration process is done.
>
> When I migrate this guest domains from B to A, everything is fine.
>
>
> Why is it so? Can it be because Xen hosts have slightly different CPUs
> (Pentium III vs Pentium IV)?


Probably.  It seems likely that the guests boot up and detect they're on a 
Pentium 4, then start using P4 specific instructions.  When they migrate to 
the P3 host these instructions will probably cause an invalid operation fault 
and cause a kernel panic :-(

The safe way to migrate to the P4 host would be to shut the domains down 
cleanly and then boot on the new host.  Save/restore and migration will not 
work...

There has occasionally been talk of either adding checks in the tools to 
prevent this kind of migration from being allowed, or a means to request that 
a domain's kernel will use the "lowest common demoninator" instruction set.  
So far, I don't think this has happened, though :-(

Cheers,
Mark

> Xen host A (guest domains have only one CPU):
>
> # cat /proc/cpuinfo
> processor       : 0
> vendor_id       : GenuineIntel
> cpu family      : 15
> model           : 4
> model name      : Intel(R) Pentium(R) 4 CPU 2.66GHz
> stepping        : 1
> cpu MHz         : 2666.704
> cache size      : 1024 KB
> fdiv_bug        : no
> hlt_bug         : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 5
> wp              : yes
> flags           : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36
> clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc pni
> monitor ds_cpl cid cx16 xtpr
> bogomips        : 5337.19
>
> processor       : 1
> vendor_id       : GenuineIntel
> cpu family      : 15
> model           : 4
> model name      : Intel(R) Pentium(R) 4 CPU 2.66GHz
> stepping        : 1
> cpu MHz         : 2666.704
> cache size      : 1024 KB
> fdiv_bug        : no
> hlt_bug         : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 5
> wp              : yes
> flags           : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36
> clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc pni
> monitor ds_cpl cid cx16 xtpr
> bogomips        : 5337.19
>
>
>
> Xen host B:
>
> # cat /proc/cpuinfo
> processor       : 0
> vendor_id       : GenuineIntel
> cpu family      : 6
> model           : 11
> model name      : Intel(R) Pentium(R) III CPU family      1266MHz
> stepping        : 1
> cpu MHz         : 1260.597
> cache size      : 512 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 tsc msr pae mce cx8 apic mtrr mca cmov pat pse36
> mmx fxsr sse
> bogomips        : 2522.07

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users