Xen users - Dec 2005 - Using the -xen kernel rather than -xen0/U was Poor hard disk performance on xen-3/dom0

>users really should be using the -xen kernel rather than -xen0/U.
This is very good advice, and easy to follow.  If you are building Xen
for testing or production use the "xen" kenel.  It is much more like
the kenel in most distributions, everything compiled as a module.

Just edit the top level Makefile so that this line:

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

looks like this

KERNELS ?= linux-2.6-xen

You will get a single kernel and modules which can be used for both
Domain0 and all DomainUs.

Copy the modules directory  /lib/modules/2.6.whatever-xen to the
/lib/modules directory of your VM and make an initrd with mkinitrd. 
You will need to add the initrd to your grub config.

Takes a little longer to build the kernel this way, but for most
people it is much easier to deal with.

If this is not documented it should be.  I will take a look at the
wiki over the weekend and add something if it is not already there.

David



On 12/30/05, Eric S. Johansson <esj@harvee.org>
wrote:
> Ian Pratt wrote:
> > I know everyone always ignores me whenever I say this, but users
really
> > should be using the -xen kernel rather than -xen0/U. The latter two
are
> > just to make build times quicker for developers. The -xen kernel has
way
> > more drivers, though built as modules, so you''ll need to make
an initrd.
>
>
>
http://www.cl.cam.ac.uk/Research/SRG/netos/xen/readmes/user/user.html#SECTION02140000000000000000
>
> section 2.4.2 building from source
> ---
>
> unless I''m missing something, the official docs say nothing about
a -xen
> kernel (and modules).  what are more appropriate instructions for building?
>
> --- eric
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>
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On Fri, 30 Dec 2005 12:33:46 -0800
David H <davidh.davidh@gmail.com> wrote:
> >users really should be using the -xen kernel rather than -xen0/U.
> 
> This is very good advice, and easy to follow.  If you are building Xen
> for testing or production use the "xen" kenel.  It is much more
like
> the kenel in most distributions, everything compiled as a module.
> 
> Just edit the top level Makefile so that this line:
> 
> KERNELS ?= linux-2.6-xen0 linux-2.6-xenU
> 
> looks like this
> 
> KERNELS ?= linux-2.6-xen
> 
> You will get a single kernel and modules which can be used for both
> Domain0 and all DomainUs.
But in typical deployments the domU''s typically have the priviliged
kernel
option and backend driver options disabled.  Sounds like this is good only for
dom0, but you could get the same benefits by cd''ing to dom0''s
source tree and
running "ARCH=xen make menuconfig" (enabling stuff as native instead
of modules
as you please). 

Or before building anything, copy over:

linux-2.6-xen-sparse/arch/xen/configs/xen_defconfig_x86_32
to
linux-2.6-xen-sparse/arch/xen/configs/xen0_defconfig_x86_32

would be easiest (but that still needs initrd for the dom0 kernel).  That at
least still maintains the slim and unpriviliged domU. 

Tim 

> 
> Copy the modules directory  /lib/modules/2.6.whatever-xen to the
> /lib/modules directory of your VM and make an initrd with mkinitrd. 
> You will need to add the initrd to your grub config.
> 
> Takes a little longer to build the kernel this way, but for most
> people it is much easier to deal with.
> 
> If this is not documented it should be.  I will take a look at the
> wiki over the weekend and add something if it is not already there.
> 
> David
> 
> 
> 
> On 12/30/05, Eric S. Johansson <esj@harvee.org> wrote:
> > Ian Pratt wrote:
> > > I know everyone always ignores me whenever I say this, but users
really
> > > should be using the -xen kernel rather than -xen0/U. The latter
two are
> > > just to make build times quicker for developers. The -xen kernel
has way
> > > more drivers, though built as modules, so you''ll need to
make an initrd.
> >
> >
> >
http://www.cl.cam.ac.uk/Research/SRG/netos/xen/readmes/user/user.html#SECTION02140000000000000000
> >
> > section 2.4.2 building from source
> > ---
> >
> > unless I''m missing something, the official docs say nothing
about a -xen
> > kernel (and modules).  what are more appropriate instructions for
building?
> >
> > --- eric
> >
> > _______________________________________________
> > 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
> 
_______________________________________________
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On Fri, Dec 30, 2005 at 12:33:46PM -0800, David H wrote:
> >users really should be using the -xen kernel rather than -xen0/U.
> 
> This is very good advice, and easy to follow.  If you are building Xen
> for testing or production use the "xen" kenel.  It is much more
like
> the kenel in most distributions, everything compiled as a module.
I really hope this will not become enforced so much that it''s the
only way to do things as personally I detest initrds and only use
kernels compiled with exactly the drivers I want.


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I used the xen 3.0 rpm''s from xensource on centos 4.1, and was kind of
surprised to see a single kernel. Now seeing these posts explains it.

Thanks guys for such a nice job :)

Would love to see more detailed explanation for building the kernel.

Would you advise to keep using the rpm or compile the kernel for production
use ?

On 12/31/05, David H <davidh.davidh@gmail.com>
wrote:
>
> >users really should be using the -xen kernel rather than -xen0/U.
>
> This is very good advice, and easy to follow.  If you are building Xen
> for testing or production use the "xen" kenel.  It is much more
like
> the kenel in most distributions, everything compiled as a module.
>
> Just edit the top level Makefile so that this line:
>
> KERNELS ?= linux-2.6-xen0 linux-2.6-xenU
>
> looks like this
>
> KERNELS ?= linux-2.6-xen
>
> You will get a single kernel and modules which can be used for both
> Domain0 and all DomainUs.
>
> Copy the modules directory  /lib/modules/2.6.whatever-xen to the
> /lib/modules directory of your VM and make an initrd with mkinitrd.
> You will need to add the initrd to your grub config.
>
> Takes a little longer to build the kernel this way, but for most
> people it is much easier to deal with.
>
> If this is not documented it should be.  I will take a look at the
> wiki over the weekend and add something if it is not already there.
>
> David
>
>
>
> On 12/30/05, Eric S. Johansson <esj@harvee.org> wrote:
> > Ian Pratt wrote:
> > > I know everyone always ignores me whenever I say this, but users
> really
> > > should be using the -xen kernel rather than -xen0/U. The latter
two
> are
> > > just to make build times quicker for developers. The -xen kernel
has
> way
> > > more drivers, though built as modules, so you''ll need to
make an
> initrd.
> >
> >
> >
>
http://www.cl.cam.ac.uk/Research/SRG/netos/xen/readmes/user/user.html#SECTION02140000000000000000
> >
> > section 2.4.2 building from source
> > ---
> >
> > unless I''m missing something, the official docs say nothing
about a -xen
> > kernel (and modules).  what are more appropriate instructions for
> building?
> >
> > --- eric
> >
> > _______________________________________________
> > 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
>

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