Xen users - Mar 2007 - Using the -xen kernel rather than -xen0/U

Hi List-

At 
<http://wiki.xensource.com/xenwiki/InstallationNotes#head-64f7b0db4fee44809a97a827e92fa9ed27a732a8>

I see the section entitled:

Using the -xen kernel rather than -xen0/U

which describes changing the Makefile line:

KERNELS ?= linux-2.6-xen0 linux-2.6-xenU

to read as follows:

KERNELS ?= linux-2.6-xen

But the Makefile in 3.0.2 already reads:

KERNELS ?= linux-2.6-xen

So I''m confused.

Does this mean that the default configuration has (since the wiki note 
was written) been changed so that I am, by default, using the -xen 
kernel rather than the -xen0/U kernel?

If so, what if I want to use the -xen0/U kernel?

I''m new to Xen, so please pardon me if this is a silly question.  I 
searched the archive for comments related to this but didn''t find any
in
the last year.

I will be wanting to use as many different virtual machine types as I 
can, and so I suspect that I will need different kernels for many of the 
VMs that I''ll want to run.

Will this configuration allow that?  Or will this configuration require 
that I use the same kernel for all of my VMs?

Thanks.

-Kevin

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>
<http://wiki.xensource.com/xenwiki/InstallationNotes#head-64f7b0db4fee44809
>a97a827e92fa9ed27a732a8>
>
> I see the section entitled:
>
> Using the -xen kernel rather than -xen0/U
>
> which describes changing the Makefile line:
>
> KERNELS ?= linux-2.6-xen0 linux-2.6-xenU
>
> to read as follows:
>
> KERNELS ?= linux-2.6-xen
>
> But the Makefile in 3.0.2 already reads:
>
> KERNELS ?= linux-2.6-xen
>
> So I''m confused.
>
> Does this mean that the default configuration has (since the wiki note
> was written) been changed so that I am, by default, using the -xen
> kernel rather than the -xen0/U kernel?
Yes, the configuration has changed.
> If so, what if I want to use the -xen0/U kernel?
You can change it back, building xen0/U kernels is still supported.
> I''m new to Xen, so please pardon me if this is a silly question. 
I
> searched the archive for comments related to this but didn''t find
any in
> the last year.
>
> I will be wanting to use as many different virtual machine types as I
> can, and so I suspect that I will need different kernels for many of the
> VMs that I''ll want to run.
Not really; the -xen0 or -xen kernels are both suitable to run in both dom0 
and domU.  Unless you need a particular kernel version or want to run a 
distro-provided kernel then I''d suggest that you just use the dom0
kernel
(and modules) in all domains.
> Will this configuration allow that?  Or will this configuration require
> that I use the same kernel for all of my VMs?
You can mix and match.  If you have an up-to-date Xen then pretty much any Xen 
3.0-aware kernel will run on it (modulo PAE / 64-bit settings, which will 
need to be matched).

Cheers,
Mark

-- 
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!

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Hi all,

Just installed my first server for real - an amd64 X2 AM2 3000+, which will
be going into production soon.
> Not really; the -xen0 or -xen kernels are both suitable to 
> run in both dom0 and domU.  Unless you need a particular 
> kernel version or want to run a distro-provided kernel then 
> I''d suggest that you just use the dom0 kernel (and modules) 
> in all domains.
I am concerned about memory use, are the combined -xen kernel not using more
memory than an optimized? What is the overhead by using the universal module
kernel compared to compile a static kernel with all needed parts compiled
directly in?

Thank you very much in advance, for you comments.

Best regards
Nicolai



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> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of 
> Nicolai Lang
> Sent: 04 April 2007 07:55
> To: xen-users@lists.xensource.com
> Subject: RE: [Xen-users] Using the -xen kernel rather than -xen0/U
> 
> Hi all,
> 
> Just installed my first server for real - an amd64 X2 AM2 
> 3000+, which will
> be going into production soon.
> 
> > Not really; the -xen0 or -xen kernels are both suitable to 
> > run in both dom0 and domU.  Unless you need a particular 
> > kernel version or want to run a distro-provided kernel then 
> > I''d suggest that you just use the dom0 kernel (and modules) 
> > in all domains.
> 
> I am concerned about memory use, are the combined -xen kernel 
> not using more
> memory than an optimized? What is the overhead by using the 
> universal module
> kernel compared to compile a static kernel with all needed 
> parts compiled
> directly in?
You''re looking at a small amount of extra space used - some megabytes
at
the most. 

If you''re planning to run many DomU''s, then using a stripped
down kernel
that only contains what you actually need is a good plan. But since your
system has a single processor at relatively slow speed, I''d expect
you''re not planning to run tens or hundreds of guests... ;-) So is the
saving of maybe 2-4 megabyte per guest worth the bother of figuring out
exactly which options in the kernel you actually need and how to strip
off the bits you don''t need?

--
Mats
> 
> Thank you very much in advance, for you comments.
> 
> Best regards
> Nicolai
> 
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 
> 


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Hey Mats,
> relatively slow speed, I''d expect you''re not planning to
run
> tens or hundreds of guests... ;-) So is the saving of maybe 
> 2-4 megabyte per guest worth the bother of figuring out 
> exactly which options in the kernel you actually need and how 
> to strip off the bits you don''t need?
Thanks, if it is only in that amount then I will run with the combined
kernel (if it aint broke, don''t fix it ;) ).

I will be running a max of 10 guests (more like 5-7).

But I have two extra questions that arise as I was playing with my first
guests:

1)
The dom0 is of course installed as AMD64 architechture. I was considering
installing the guests as i386, sincen I then will be able to run them under
my spare (3 year old Dell PE 1600) Xeon server. 

Is that a sensible choice? 

2)
I choose the processor because it was on stock, reasonably priced, and
because it should support HVM
(http://wiki.xensource.com/xenwiki/HVM_Compatible_Processors), but I do not
see any HVM messages during boot, nor do CPUinfo flags contain the vmx flag.

The processor is an AMD Athlon 64 X2 - 3800+ 2.0GHz BOX - AM2 EE, the
motheboard an Asus M2N-E.

Have I made a blunder? Does the HVM demand a certain motherboard? I''m
attaching cpuinfo and dmesg

Thank''s in advance.

Best regards
Nicolai




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> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of 
> Nicolai Lang
> Sent: 05 April 2007 10:54
> To: xen-users@lists.xensource.com
> Subject: RE: [Xen-users] Using the -xen kernel rather than -xen0/U
> 
> Hey Mats,
> 
> > relatively slow speed, I''d expect you''re not
planning to run
> > tens or hundreds of guests... ;-) So is the saving of maybe 
> > 2-4 megabyte per guest worth the bother of figuring out 
> > exactly which options in the kernel you actually need and how 
> > to strip off the bits you don''t need?
> 
> Thanks, if it is only in that amount then I will run with the combined
> kernel (if it aint broke, don''t fix it ;) ).
> 
> I will be running a max of 10 guests (more like 5-7).
> 
> But I have two extra questions that arise as I was playing 
> with my first
> guests:
> 
> 1)
> The dom0 is of course installed as AMD64 architechture. I was 
> considering
> installing the guests as i386, sincen I then will be able to 
> run them under
> my spare (3 year old Dell PE 1600) Xeon server. 
> 
> Is that a sensible choice? 
At present (3.0.4), para-virtual guests will need to run at the same
"bitness" as the Dom0, so you either use 64-bit all over, or 32-bit. 

HVM (fully virtualized) guests can be whatever bitness is less or equal
to Dom0. 

There is little difference between running 32 and 64-bit (most of it is
marginally to the advantage of 64-bit, but unless you really need huge
amounts of memory, I''d say you wouldn''t be able to tell any
difference
other than by specific benchmarks). 
> 
> 2)
> I choose the processor because it was on stock, reasonably priced, and
> because it should support HVM
> (http://wiki.xensource.com/xenwiki/HVM_Compatible_Processors),
>  but I do not
> see any HVM messages during boot, nor do CPUinfo flags 
> contain the vmx flag.
> 
> The processor is an AMD Athlon 64 X2 - 3800+ 2.0GHz BOX - AM2 EE, the
> motheboard an Asus M2N-E.
/proc/cpuinfo should contain "svm" (but not "vmx", as
that''s the Intel
name for their corresponding technology). ["svm" is in your
cpuinfo.txt].  

All AM2 processors are HVM compatible except if they are called
"Sempron". 

--
Mats
> 
> Have I made a blunder? Does the HVM demand a certain motherboard?
I''m
> attaching cpuinfo and dmesg
> 
> Thank''s in advance.
> 
> Best regards
> Nicolai
> 
> 


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Hi Mats, 

Once again I thank you for your replies, it is very nice with a group of
experts to lean upon :)
> There is little difference between running 32 and 64-bit 
> (most of it is marginally to the advantage of 64-bit, but 
> unless you really need huge amounts of memory, I''d say you 
> wouldn''t be able to tell any difference other than by 
> specific benchmarks). 
I must say, I consider reinstalling using 32-bit, for compatibility. I just
thought that you needed amd64 binaries of everything to get full benefit of
the features like HVM and dual core.

So if the difference is neglible then it would better to run it as 32-bit
and be able to move guests between my machines.
> /proc/cpuinfo should contain "svm" (but not "vmx", as
that''s
> the Intel name for their corresponding technology). ["svm" is 
> in your cpuinfo.txt].  
Thanks. I was afraid that the store had sold me the wrong model. The VMX
flag was something I found in a different thread somewhere, it did not
mention that it was called something different by AMD.

I hope I will be able to pay back some work to the community once I am
experienced with Xen. Thank you so far for all your help.

Best regards
Nicolai



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