RE: [Xen-users] Migrating domU and virtualization extensions

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Christopher DeMarco
> Sent: 12 June 2007 04:58
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Migrating domU and virtualization extensions
> 
> On Mon, Jun 11, 2007 at 11:53:59PM +0100, Mark Williamson wrote:
> 
> > Yes, I guess you should be able to - are they both the same 
> manufacturer?  
> > Both Intel?  What models are they, actually?
> 
> Well, I don't get it.
> 
> They're both Intel Xeons, but on the old box, the contents of
> /proc/cpuinfo differ from the output of ``cpuid'' -- cpuinfo doesn't
> list vme/vmx, but cpuid does.  Also, /proc/cpuinfo on the new system
> lists *8* cores, but I coulda sworn that Dell's deal was for 2
> dual-core Xeons.  Gotta lookit that onsite tomorrow.

8 cores would be "2 sockets * 2 cores * 2 hyperthreads" perhaps?

> 
> But anyway, here's a diff against ``cpuid'' on both boxen.  "onion" is
> the old one, "wilbur" is the new one:
> 
> --- onion       2007-06-11 23:48:55.000000000 -0400
> +++ wilbur      2007-06-11 23:49:42.000000000 -0400
> @@ -1,35 +1,35 @@
>   eax in    eax      ebx      ecx      edx
> -00000000 00000005 756e6547 6c65746e 49656e69
> -00000001 00000f41 01020800 0000641d bfebfbff
> -00000002 605b5001 00000000 00000000 007c7040
> +00000000 00000006 756e6547 6c65746e 49656e69
> +00000001 00000f64 03040800 0000e4bd bfebfbff
> +00000002 605b5001 00000000 00000000 007d7040
>  00000003 00000000 00000000 00000000 00000000
> -00000004 00004121 01c0003f 0000001f 00000000
> +00000004 04004121 01c0003f 0000001f 00000000
>  00000005 00000040 00000040 00000000 00000000
> +00000006 00000000 00000000 00000000 00000000
>  80000000 80000008 00000000 00000000 00000000
> -80000001 00000000 00000000 00000000 20100000
> +80000001 00000000 00000000 00000001 20100000
>  80000002 20202020 20202020 20202020 20202020
>  80000003 6e492020 286c6574 58202952 286e6f65
> -80000004 20294d54 20555043 30382e32 007a4847
> +80000004 20294d54 20555043 30302e33 007a4847
>  80000005 00000000 00000000 00000000 00000000
> -80000006 00000000 00000000 04006040 00000000
> +80000006 00000000 00000000 08006040 00000000
>  80000007 00000000 00000000 00000000 00000000
>  80000008 00003024 00000000 00000000 00000000
>  
> -Vendor ID: "GenuineIntel"; CPUID level 5
> +Vendor ID: "GenuineIntel"; CPUID level 6
>  
>  Intel-specific functions:
> -Version 00000f41:
> +Version 00000f64:
>  Type 0 - Original OEM
>  Family 15 - Pentium 4
>  Extended family 0
> -Model 4 - 
> -Stepping 1
> +Model 6 - 
> +Stepping 4
>  Reserved 0
>  
> -Extended brand string: "                  Intel(R) Xeon(TM) CPU
> 2.80GHz"
> +Extended brand string: "                  Intel(R) Xeon(TM) CPU
> 3.00GHz"
>  CLFLUSH instruction cache line size: 8
> -Initial APIC ID: 1
> -Hyper threading siblings: 2
> +Hyper threading siblings: 4

Yup, you've got 2 hyperthreads per core -> 8 "cores" to Linux.
Hyperthreads CAN help Xen in the sense that you could dedicate a
hyperthread to Dom0, giving the CPU performance of the core to run DomU
most of the time, but also avoiding a "world switch" when going to dom0,
as it's still got it's dedicated core - but you do loose a little
compared to giving a physical full core to Dom0 of course. 
>  
>  Feature flags bfebfbff:
>  FPU    Floating Point Unit
> @@ -67,5 +67,5 @@
>  60: unknown TLB/cache descriptor
>  40: No 2nd-level cache, or if 2nd-level cache exists, no 3rd-level
> cache
>  70: Trace cache: 12K-micro-op, 4-way set assoc
> -7c: 2nd-level cache: 1MB, 8-way set assoc, sectored, 64 byte line
> size
> -Processor serial: 0000-0F41-0000-0000-0000-0000
> +7d: unknown TLB/cache descriptor
> +Processor serial: 0000-0F64-0000-0000-0000-0000

It doesn't look to me like there are any "important" differences, such
as SSE2 on one but not on the other. These are the type of things that
could cause problems when migrating. 

--
Mats
> 
> 
> > etc).  They get horribly confused if live migration happens 
> - if they 
> > suddenly find themselves migrated to a system without the 
> capabilities they 
> > were expecting, receive invalid operation exceptions, and 
> probably crash.
> 
> Does this mean that an offline migration will work?  If I can just
> shut down the domU and then ``tar | nc | tar'', I'm thrilled.  VMWare
> won't run a VM from the old system on the new one.
> 
> 
> -- 
> Christopher DeMarco <demarco@xxxxxxxx>
> Information Technology Supervisor
> MAYA Group
> +1-412-488-2900
> 
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> 
> 
> 



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