Xen users - Jun 2006 - Moved from Xen 2 to Xen 3... some questions..

Hi,

Ive been using Xen2 for ages, and it great, but ive decided to go to Xen 3.

Ive got it working, but I want to ask a couple of questions about it.

1. There no longer seems to be a seperate DomU and Dom0 built when I build
from source. Is this the new policy? this would suit me, as I always used
Xen0 kernels in my guest domains anyway.

2. Ive got me a vmx (vanderpool / intel virtualization tech) enabled
processor (as shown in cpuflags in /proc/cpuinfo) - can Xen just use it from
the default build (make world), or do I have to set any flags at compile
time? it didnt winge about missing LibVNCServer, so I assume it wasnt
built... ive looked in the manual, but it doesnt seem to say what I need to
set to build a vmx version.

3. Still relating to VMX - how can I determine if my bios supports VMX? its
a Compaq machine. Does the presence of vmx in /proc/cpuinfo indicate the
bios supports it? there are no options in the BIOS about vmx (there is one
about NX flag - i realise thats the no execute flag, but that is where I
would expect any VMX options to be). Do all bios''s that support VMX
have an
option to enbale / disable it?

If its not enabled, is is possible to ''hack'' the bios image to
enable it? (i
once used a tool to enable IRDA on a bios for a gigabyte motherboard, so I
know bios rom images can be tampered with!)

4. The processor in the new box is dual core- do I need to build a SMP
version of the Xen hypervisor / Linux kernel to take advantage of this? or
does the hypervisor deal with this side of things, and allocate processors
to domains?

5. Is there ANY way to see the pre-linux-kernel messages from boot (the
messages from the hypervisor)? they scroll past so quickly I cannot read
them, then if I get a kernel panic when the Linux kernel starts, I cannot
see what the hypervisor was saying. It turned out to be lack of sata drivers
in the kernel (they were modules), but that was guesswork. Im sure the Xen
boot messages would tell me what hardware it had picked up.

6. When I was trying to build a custom kernel (with the sata drivers in), i
tried the usual
make ARCH=xen menuconfig
in the linux source dir, but it gave an error (something about no such
target or somesuch).
Is this no longer nescesary? it worked OK when I ommitted the ARCH=xen, but
I didnt proceed as I wasnt sure if it would compile in the Xen stuff...
whats going on???

(I got it booting in the end by making a ramdisk, so these questions are
academic, but I like to understand whats going on)

Finally, if the noreboot option is in the hypervisor parameter lines in grub
config, does that prevent software reboot from working in Dom0? ive remotely
crashed my Xen box on a reboot, and am hoping thats what it is! (it was its
first reboot after booting Dom0 and I still had noreboot in from when I was
trying to get Dom0 up)

thanks in advance for any insight :)

George


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

On Thu, Jun 01, 2006 at 12:25:35PM +0100, George Styles wrote:
> Ive got it working, but I want to ask a couple of questions about it.
  I can''t help with all of them, but I''ll answer a couple of
your
 questions.
>    1. There no longer seems to be a seperate DomU and Dom0 built when I
build
>    from source. Is this the new policy? this would suit me, as I always
used
>    Xen0 kernels in my guest domains anyway.
  Yes.  You can still build seperate kernels if you wish, but it is no
 longer the default.

>    5. Is there ANY way to see the pre-linux-kernel messages from boot (the
>    messages from the hypervisor)? they scroll past so quickly I cannot read
>    them, then if I get a kernel panic when the Linux kernel starts, I
cannot
>    see what the hypervisor was saying. It turned out to be lack of sata
>    drivers in the kernel (they were modules), but that was guesswork. Im
sure
>    the Xen boot messages would tell me what hardware it had picked up.
  xm dmesg
>    6. When I was trying to build a custom kernel (with the sata drivers
in),
>    i tried the usual
>    make ARCH=xen menuconfig
>    in the linux source dir, but it gave an error (something about no such
>    target or somesuch).
>    Is this no longer nescesary? it worked OK when I ommitted the ARCH=xen,
>    but I didnt proceed as I wasnt sure if it would compile in the Xen
>    stuff... whats going on???
  Yes Xen is no longer a sub-arch, and has been merged into the normal
  system.  So you can exclude it as you did with safety.

Steve
-- 
http://www.steve.org.uk/

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

HI George,
I''ll answer some of your questions, some must be takenby others.
(maybe it would be helpful to split so many questions into multiple
mails).

On 6/1/06, George Styles <ripnetuk@gmail.com>
wrote:
> Hi,
>
> Ive been using Xen2 for ages, and it great, but ive decided to go to Xen 3.
>
> Ive got it working, but I want to ask a couple of questions about it.
>
> 1. There no longer seems to be a seperate DomU and Dom0 built when I build
> from source. Is this the new policy? this would suit me, as I always used
> Xen0 kernels in my guest domains anyway.
This is the new policy.
> [...]
> 5. Is there ANY way to see the pre-linux-kernel messages from boot (the
> messages from the hypervisor)? they scroll past so quickly I cannot read
> them, then if I get a kernel panic when the Linux kernel starts, I cannot
> see what the hypervisor was saying. It turned out to be lack of sata
drivers
> in the kernel (they were modules), but that was guesswork. Im sure the Xen
> boot messages would tell me what hardware it had picked up.
did you try "xm dmesg" ?

> 6. When I was trying to build a custom kernel (with the sata drivers in), i
> tried the usual
> make ARCH=xen menuconfig
> in the linux source dir, but it gave an error (something about no such
> target or somesuch).
> [...]
You''ll find info on that int the README file. Please come back with
questions after reading this.


hth,
Henning

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

> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of Steve Kemp
> Sent: 01 June 2006 12:35
> To: george@ripnet.co.uk
> Cc: xen-users@lists.xensource.com
> Subject: Re: [Xen-users] Moved from Xen 2 to Xen 3... some questions..
> 
> On Thu, Jun 01, 2006 at 12:25:35PM +0100, George Styles wrote:
> 
> > Ive got it working, but I want to ask a couple of questions 
> about it.
> 
>   I can''t help with all of them, but I''ll answer a couple
of
> your  questions.
> 
> >    1. There no longer seems to be a seperate DomU and Dom0 
> built when I build
> >    from source. Is this the new policy? this would suit me, 
> as I always used
> >    Xen0 kernels in my guest domains anyway.
> 
>   Yes.  You can still build seperate kernels if you wish, but 
> it is no  longer the default.
> 
> 
> >    5. Is there ANY way to see the pre-linux-kernel messages 
> from boot (the
> >    messages from the hypervisor)? they scroll past so 
> quickly I cannot read
> >    them, then if I get a kernel panic when the Linux kernel 
> starts, I cannot
> >    see what the hypervisor was saying. It turned out to be 
> lack of sata
> >    drivers in the kernel (they were modules), but that was 
> guesswork. Im sure
> >    the Xen boot messages would tell me what hardware it had 
> picked up.
> 
>   xm dmesg
> 
> >    6. When I was trying to build a custom kernel (with the 
> sata drivers in),
> >    i tried the usual
> >    make ARCH=xen menuconfig
> >    in the linux source dir, but it gave an error (something 
> about no such
> >    target or somesuch).
> >    Is this no longer nescesary? it worked OK when I 
> ommitted the ARCH=xen,
> >    but I didnt proceed as I wasnt sure if it would compile 
> in the Xen
> >    stuff... whats going on???
> 
>   Yes Xen is no longer a sub-arch, and has been merged into the normal
>   system.  So you can exclude it as you did with safety.
I think technically, you should have said "Xen is NOW A SUBARCH, no
longer a separate architecture", so you need to set the
"Subarchitecture" inside the x86 processor choice in the Linux .config
(which will be done automagically if you use Xen from the normal source
files). 

--
Mats
> 
> Steve
> --
> http://www.steve.org.uk/
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 

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

George, 
 
Steve Kemp kindly answered a few of your questions. 
 
I''ll try to answer some of the others, to the best of my abilities.... 
 
1. Was answered by Steve. 
 
2. HVM support is automatically built into the kernel. So, as long as
you have a processor that supports AMD SVM or Intels VMX technology, Xen
will do what it needs to. LibVNCServer is needed by QEMU if you want to
use VNC to view your virtual machine - you need EITHER VNC or SDL to see
what''s going on on a fully-virtualized machine - unless you want to
connect to the virtual machine through some other networked means, of
course - you can use SSH to connect to a Linux machine (or a Windows
machine if you can find a SSH service to run on it), but that may not be
what you WANT to do... And for debugging the boot process, it can be
quite useful to see what''s going on!
 
If it works, you''ll see the Intel version of this:
(XEN) Initializing CPU#0
(XEN) Detected 2785.881 MHz processor.
(XEN) CPU0: AMD Flush Filter disabled
(XEN) CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line)
(XEN) CPU: L2 Cache: 1024K (64 bytes/line)
(XEN) CPU 0(2) -> Core 0
(XEN) AMD SVM Extension is enabled for cpu 0.
(XEN) Intel machine check architecture supported.
(XEN) Intel machine check reporting enabled on CPU#0.
(XEN) CPU0: AMD Athlon(tm) 64 FX-62 Dual Core Processor stepping 02

Where it says "AMD SVM Extension is enabled for cpu 0" it should say
"Intel VMX Extension enabled" (or something very similar). If you
don''t
see that in the boot messages, then you haven''t got VMX enabled in the
processor, and you need to do something to fix it. 
 
3. I don''t know if all BIOS has a option for this or not - I know one
of
our machines has the option the wrong way around - Set it to disabled
and it works! If your BIOS doesn''t do the right thing, you''d
think by
now that the latest BIOS for that motherboard would have the feature -
unless it''s so old that the manufacturer no longer updates the BIOS
unless REALLY necessary of course... Since I work with AMD hardware, and
my motherboards are all internal AMD prototypes, I can''t really say for
Intel products... See above to know if it works or not... 
 
4. Yes, to be able to use a dual core processor, you should compile Xen
as SMP, but I think that''s the default today anyways - whether you also
compile Dom0 as SMP is up to you. Depending on how much traffic you get
through Dom0, it may make sense to do so, but it may also cause more
load on the processors from Dom0 which prevents some other domain from
running - and that may be more important - depends on what you do in
your system, really...  As to allocating processors to domains, the
Hypervisor will allocate processors for the domain - but you can tell it
what to do. Many people recommend setting a particular processor to be
Dom0 always, and not let DomU''s run on that processor ever. That
reduces
the time to switch between DomU and Dom0. 
 
5, 6 are answered by Steve.
 
Non-numbered question on "noreboot": Yes, if you shutdown the system
with noreboot on the command-line, it will not restart after you shut it
down...
--
Mats


________________________________

	From: xen-users-bounces@lists.xensource.com
[mailto:xen-users-bounces@lists.xensource.com] On Behalf Of George
Styles
	Sent: 01 June 2006 12:26
	To: xen-users@lists.xensource.com
	Subject: [Xen-users] Moved from Xen 2 to Xen 3... some
questions..
	
	
	Hi,
	
	Ive been using Xen2 for ages, and it great, but ive decided to
go to Xen 3.
	
	Ive got it working, but I want to ask a couple of questions
about it.
	
	1. There no longer seems to be a seperate DomU and Dom0 built
when I build from source. Is this the new policy? this would suit me, as
I always used Xen0 kernels in my guest domains anyway. 
	
	2. Ive got me a vmx (vanderpool / intel virtualization tech)
enabled processor (as shown in cpuflags in /proc/cpuinfo) - can Xen just
use it from the default build (make world), or do I have to set any
flags at compile time? it didnt winge about missing LibVNCServer, so I
assume it wasnt built... ive looked in the manual, but it doesnt seem to
say what I need to set to build a vmx version. 
	
	3. Still relating to VMX - how can I determine if my bios
supports VMX? its a Compaq machine. Does the presence of vmx in
/proc/cpuinfo indicate the bios supports it? there are no options in the
BIOS about vmx (there is one about NX flag - i realise thats the no
execute flag, but that is where I would expect any VMX options to be).
Do all bios''s that support VMX have an option to enbale / disable it? 
	
	If its not enabled, is is possible to ''hack'' the bios image
to
enable it? (i once used a tool to enable IRDA on a bios for a gigabyte
motherboard, so I know bios rom images can be tampered with!)
	
	4. The processor in the new box is dual core- do I need to build
a SMP version of the Xen hypervisor / Linux kernel to take advantage of
this? or does the hypervisor deal with this side of things, and allocate
processors to domains? 
	
	5. Is there ANY way to see the pre-linux-kernel messages from
boot (the messages from the hypervisor)? they scroll past so quickly I
cannot read them, then if I get a kernel panic when the Linux kernel
starts, I cannot see what the hypervisor was saying. It turned out to be
lack of sata drivers in the kernel (they were modules), but that was
guesswork. Im sure the Xen boot messages would tell me what hardware it
had picked up. 
	
	6. When I was trying to build a custom kernel (with the sata
drivers in), i tried the usual
	make ARCH=xen menuconfig
	in the linux source dir, but it gave an error (something about
no such target or somesuch). 
	Is this no longer nescesary? it worked OK when I ommitted the
ARCH=xen, but I didnt proceed as I wasnt sure if it would compile in the
Xen stuff... whats going on???
	
	(I got it booting in the end by making a ramdisk, so these
questions are academic, but I like to understand whats going on) 
	
	Finally, if the noreboot option is in the hypervisor parameter
lines in grub config, does that prevent software reboot from working in
Dom0? ive remotely crashed my Xen box on a reboot, and am hoping thats
what it is! (it was its first reboot after booting Dom0 and I still had
noreboot in from when I was trying to get Dom0 up) 
	
	thanks in advance for any insight :)
	
	George
	



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

Thank you very much all of you... all my questions answered in a matter of
hours...

Loving xen

g


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