Domain 0 SMP

Domain 0 SMP

[Remi Broemeling]

Hey there.  I'm having an issue; and I am not sure if it is an issue
with Xen or simply that I don't understand what I am doing.

Specifically, I have a number of servers that we want to virtualize --
I've tried UML, but was rather unimpressed with the performance, and
hence want to give Xen a try.  These servers are SMP Xeon boxes, with
about 1GB-1.5GB of RAM each.  Just standard server boxes, really;
nothing special about them.

I've got all the pre-reqs setup (we run Debian woody, so some of it
was a pain to get to the right versions, but I've managed, with stow
and backports.org), and the "check" script that comes with the Xen
binaries package completes with no errors found.

Now, I want to compile custom -xen0 and -xenU kernels.  It is my
understanding that -xen0 is the "master" kernel, that supports the
hardware, and then the -xenU kernels are the virtual kernels that live
inside -xen0.  Hence, I want to have a -xen0 kernel that supports all
the necessary hardware for the box, but the -xenU kernel just requires
the frontend drivers to connect to the hardware that -xen0 shares with
the backend drivers, correct?

My problem is with the -xen0 kernel -- specifically, I can't find any
place to _enable_ SMP in it.  I know that SMP is not currently
possible within -xenU kernels; which is fine.  I don't need SMP within
the virtual machines.  However, I _do_ need it in the -xen0 kernel,
and the option isn't there in "make ARCH=xen xconfig"

What am I doing wrong?  How can I enable SMP for the domain 0 Xen
kernel?  I note that the documentation lists a 'nosmp' argument that
can be passed as an argument to a -xen0 kernel to turn _off_ SMP.  Is
SMP perhaps just "always-on"?

(I am using xen-2.0.4-src, and am working in the 'linux-2.6.10-xen0'
directory created by a call to 'make kernels')

Thanks.


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Re: Domain 0 SMP

[Rik van Riel]

On Thu, 3 Mar 2005, Remi Broemeling wrote:

> My problem is with the -xen0 kernel -- specifically, I can't find any
> place to _enable_ SMP in it.  I know that SMP is not currently
> possible within -xenU kernels; which is fine.

> (I am using xen-2.0.4-src, and am working in the 'linux-2.6.10-xen0'
> directory created by a call to 'make kernels')

The -unstable tree does support SMP guests.

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan


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Re: Domain 0 SMP

[Christian Limpach]

On Thu, 3 Mar 2005 12:08:35 -0700, Remi Broemeling
<rbroemeling@gmail.com> wrote:
> My problem is with the -xen0 kernel -- specifically, I can't find any
> place to _enable_ SMP in it.  I know that SMP is not currently
> possible within -xenU kernels; which is fine.  I don't need SMP within
> the virtual machines.  However, I _do_ need it in the -xen0 kernel,
> and the option isn't there in "make ARCH=xen xconfig"

No, xen 2.0 doesn't support SMP in virtual machines.  dom0 is a
virtual machine with some additional privileges, but as far as SMP
support is concerned it is just another virtual machine.

> What am I doing wrong?  How can I enable SMP for the domain 0 Xen
> kernel?  I note that the documentation lists a 'nosmp' argument that
> can be passed as an argument to a -xen0 kernel to turn _off_ SMP.  Is
> SMP perhaps just "always-on"?

The 'nosmp' option is passed to xen itself (not dom0) and would
disable smp support in xen.  That's not what you want.  Because with
smp support enabled in xen, you will make good use of your smp
hardware as soon as you have more than one virtual machine, by putting
them on different cpus (see cpu= option in config file and xm pincpu).

    christian


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Re: Domain 0 SMP

[Mark Williamson]

> My problem is with the -xen0 kernel -- specifically, I can't find any
> place to _enable_ SMP in it.  I know that SMP is not currently
> possible within -xenU kernels; which is fine.  I don't need SMP within
> the virtual machines.  However, I _do_ need it in the -xen0 kernel,
> and the option isn't there in "make ARCH=xen xconfig"

All domains are equal regarding their interface to the CPU - Xen is 
responsible for sharing out the CPU.  Xen 2.x only supports SMP domains, 
hence all domains must be SMP.  Xen 3.0 will support SMP domains (dom0 and 
domU), this is being developed in the unstable tree.

Xen itself supports SMP, so you can put domains on each CPU.

> What am I doing wrong?  How can I enable SMP for the domain 0 Xen
> kernel?  I note that the documentation lists a 'nosmp' argument that
> can be passed as an argument to a -xen0 kernel to turn _off_ SMP.  Is
> SMP perhaps just "always-on"?

nosmp is to tell Xen not to use smp (i.e. run domains just on one CPU).

HTH,
Mark

> (I am using xen-2.0.4-src, and am working in the 'linux-2.6.10-xen0'
> directory created by a call to 'make kernels')
>
> Thanks.
>
>
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Re: Domain 0 SMP

[Mark Williamson]

> responsible for sharing out the CPU.  Xen 2.x only supports SMP domains,
> hence all domains must be SMP.

*bangs head against desk, plugs the coffee drip back in*

That should have read: 2.x only supports UP domains, hence all domains must be 
UP.

Thanks to Brian for pointing this out to me :-)

Cheers,
Mark

> Xen 3.0 will support SMP domains (dom0 and 
> domU), this is being developed in the unstable tree.
>
> Xen itself supports SMP, so you can put domains on each CPU.
>
> > What am I doing wrong?  How can I enable SMP for the domain 0 Xen
> > kernel?  I note that the documentation lists a 'nosmp' argument that
> > can be passed as an argument to a -xen0 kernel to turn _off_ SMP.  Is
> > SMP perhaps just "always-on"?
>
> nosmp is to tell Xen not to use smp (i.e. run domains just on one CPU).
>
> HTH,
> Mark
>
> > (I am using xen-2.0.4-src, and am working in the 'linux-2.6.10-xen0'
> > directory created by a call to 'make kernels')
> >
> > Thanks.
> >
> >
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> > Xen-devel mailing list
> > Xen-devel@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/xen-devel
>
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