Xen users - Mar 2009 - Paravirtualized vs HVM - how big is the performance gap?

We are currently in the situation of needing to use Scientific Linux 4.x
(a RHEL derivative) in paravirtualized mode. The problem is that the
virt-install command/libvirt don''t support installing Scientific Linux
4.x (only 5.x) so I''m having great trouble installing SL4.x in a
paravirt domU.

I see 3 possibilities but don''t really know if they are realistic so
need people''s thoughts on them:

* Find a way to install SL4.x in a HVM domU and then convert that domU
to paravirt mode (I''m trying this now but with no success)

* There is some technique to allow booting of paravirt VMs off of .iso
images or over PXE (or any other method that could lead to a Kickstart
installation)?

* Just run 4.x in HVM mode - roughly how big is the performance impact
and how could I minimise it?

The hardware we''re running this on supports AMD-V virtualisation, the
domain0 OS is Scientific Linux 5.3 x86_64.

Thanks

Tim Edwards

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On Fri, Mar 27, 2009 at 4:08 PM, Tim Edwards <tedwards@it.dcs.ch>
wrote:
> I see 3 possibilities but don''t really know if they are realistic
so
> need people''s thoughts on them:
>
> * Find a way to install SL4.x in a HVM domU and then convert that domU
> to paravirt mode (I''m trying this now but with no success)
>
If you have problems converting, try my method
http://lists.xensource.com/archives/html/xen-users/2009-03/msg00372.html

It needs /boot and "/" to be on the same partition (e.g. hda1) on HVM
install, without LVM, to simplify things. I haven''t tested it for SL 4
(don''t have an OS template handy atm), but it should work with the
differences that the kernel package is kernel-xenU instead of
kernel-xen, and the source tree is HVM installation instead of OS
template, and hda1 instead of sda1.
Let me know if you experience problems.
> * There is some technique to allow booting of paravirt VMs off of .iso
> images or over PXE (or any other method that could lead to a Kickstart
> installation)?
Try http://wiki.centos.org/HowTos/Xen/InstallingCentOSDomU
domU installation kernel and initrd is from
http://mirror.centos.org/centos/4/os/i386/images/xen/
kickstart installation URL is http://mirror.centos.org/centos/4/os/i386/
>
> * Just run 4.x in HVM mode - roughly how big is the performance impact
> and how could I minimise it?
Should be pretty big. I haven''t tested HVM Linux specifically (never
needed one), but you can look at my numbers for Windows HVM on
opensolaris dom0:

Disk peformance, command line : dd if=/dev/zero of=test2G bs=1M count=2048
without GPLPV : 6.6 MB/s
with GPLPV : 12.1 MB/s
Linux PV : 24.6 MB/s

Network performance, with iperf:
Without GPLPV : dom0->domU 38.8 Mbps, domU->dom0 24.4 Mbps,
With GPLPV : dom0->domU 148 Mbps, domU->dom0 446 Mbps
Linux PV : dom0->domU 556 Mbps, domU->dom0 631Mbps

Regards,

Fajar

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On Fri, Mar 27, 2009 at 10:08:05AM +0100, Tim Edwards
wrote:
> We are currently in the situation of needing to use Scientific Linux 4.x
> (a RHEL derivative) in paravirtualized mode. The problem is that the
> virt-install command/libvirt don''t support installing Scientific
Linux
> 4.x (only 5.x) so I''m having great trouble installing SL4.x in a
> paravirt domU.
> 
> I see 3 possibilities but don''t really know if they are realistic
so
> need people''s thoughts on them:
> 
> * Find a way to install SL4.x in a HVM domU and then convert that domU
> to paravirt mode (I''m trying this now but with no success)
> 
> * There is some technique to allow booting of paravirt VMs off of .iso
> images or over PXE (or any other method that could lead to a Kickstart
> installation)?
> 
> * Just run 4.x in HVM mode - roughly how big is the performance impact
> and how could I minimise it?
> 
> The hardware we''re running this on supports AMD-V virtualisation,
the
> domain0 OS is Scientific Linux 5.3 x86_64.
> 
Old tutorial from 2006:
http://people.redhat.com/riel/RHEL4-Xen-HOWTO

http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Virtualization_Guide/chap-Virtualization-Compatibility_of_host_and_guest_combinations.html

"Supported para-virtualized guest"
"Red Hat Enterprise Linux 4 x86 Update 5 and higher	Optimized"

So you should be able to install RHEL4 (or SL4) PV domU (it includes
kernel-xenU).

-- Pasi

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Hi Tim

I have a dom0 server running SL 5.1 (i386), and I was able to install a 
SL 4.7 (i386) domU.
When you say virt-install command/libvirt do not allow, what are the 
errors you are getting?

Cheers,
N.
 
Tim Edwards wrote:
> We are currently in the situation of needing to use Scientific Linux 4.x
> (a RHEL derivative) in paravirtualized mode. The problem is that the
> virt-install command/libvirt don''t support installing Scientific
Linux
> 4.x (only 5.x) so I''m having great trouble installing SL4.x in a
> paravirt domU.
>
> I see 3 possibilities but don''t really know if they are realistic
so
> need people''s thoughts on them:
>
> * Find a way to install SL4.x in a HVM domU and then convert that domU
> to paravirt mode (I''m trying this now but with no success)
>
> * There is some technique to allow booting of paravirt VMs off of .iso
> images or over PXE (or any other method that could lead to a Kickstart
> installation)?
>
> * Just run 4.x in HVM mode - roughly how big is the performance impact
> and how could I minimise it?
>
> The hardware we''re running this on supports AMD-V virtualisation,
the
> domain0 OS is Scientific Linux 5.3 x86_64.
>
> Thanks
>
> Tim Edwards
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>   

-- 
=============================================Nuno Ricardo Santos Loureiro da
Silva Ferreira

NMR Spectroscopy Research Group
Bijvoet Center for Biomolecular Research
Utrecht University
Bloembergen gebouw
Padualaan 8, 3584 CH Utrecht
The Netherlands

P: +31.(0)30.253 9932
F: +31.(0)30.253 2652
E: n.l.ferreira@uu.nl
W: http://nmr.chem.uu.nl
=============================================

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Ferreira, N. L. (Nuno) wrote:
> Hi Tim
> 
> I have a dom0 server running SL 5.1 (i386), and I was able to install a
> SL 4.7 (i386) domU.
> When you say virt-install command/libvirt do not allow, what are the
> errors you are getting?
> 
> Cheers,
> N.
I''ve looked into the virt-install command in more detail now. The
problem is that the SL4.3 installation tree has no images/xen/
directory, whereas more recent RHEL/SL 4.x (eg. 4.6, 4.7) do. The
virt-install expects to retrieve a vmlinuz and initrd.img from there.
(The error is "Invalid file location given: No such file or
directory")

Tim Edwards

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Ok.
So go for a SL 4.7 installation, unless you really need the 4.3 one.

Good luck.

N.

P.S. It is from experience (and talknig with some sysadmins) that you 
are better off putting a dom0 with a SL OS. Go for a centOS, fedora or 
RHEL based one, and then build your SL machines on top.

Tim Edwards wrote:
> Ferreira, N. L. (Nuno) wrote:
>   
>> Hi Tim
>>
>> I have a dom0 server running SL 5.1 (i386), and I was able to install a
>> SL 4.7 (i386) domU.
>> When you say virt-install command/libvirt do not allow, what are the
>> errors you are getting?
>>
>> Cheers,
>> N.
>>     
>
> I''ve looked into the virt-install command in more detail now. The
> problem is that the SL4.3 installation tree has no images/xen/
> directory, whereas more recent RHEL/SL 4.x (eg. 4.6, 4.7) do. The
> virt-install expects to retrieve a vmlinuz and initrd.img from there.
> (The error is "Invalid file location given: No such file or
directory")
>
> Tim Edwards
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>   

-- 
=============================================Nuno Ricardo Santos Loureiro da
Silva Ferreira

NMR Spectroscopy Research Group
Bijvoet Center for Biomolecular Research
Utrecht University
Bloembergen gebouw
Padualaan 8, 3584 CH Utrecht
The Netherlands

P: +31.(0)30.253 9932
F: +31.(0)30.253 2652
E: n.l.ferreira@uu.nl
W: http://nmr.chem.uu.nl
=============================================

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Ferreira, N. L. (Nuno) wrote:
> Ok.
> So go for a SL 4.7 installation, unless you really need the 4.3 one.
> 
> Good luck.
> 
> N.
> 
> P.S. It is from experience (and talknig with some sysadmins) that you
> are better off putting a dom0 with a SL OS. Go for a centOS, fedora or
> RHEL based one, and then build your SL machines on top.
Unfortunately I''ve found out that I can''t - we need to run
certain
custom software that''s only certified and supported on SL 4.3.
I''m going
to try copying the images/xen/ directory from 4.5 (the earliest version
that has that) into my 4.3 tree.

Tim Edwards

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2009/3/27 Tim Edwards <tedwards@it.dcs.ch>:
> Ferreira, N. L. (Nuno) wrote:
>> Ok.
>> So go for a SL 4.7 installation, unless you really need the 4.3 one.
> Unfortunately I''ve found out that I can''t - we need to
run certain
> custom software that''s only certified and supported on SL 4.3.
I''m going
> to try copying the images/xen/ directory from 4.5 (the earliest version
> that has that) into my 4.3 tree.
... and running it under Xen instead of bare-metal wouldn''t break
certification/support?
Seriously, if certification is your main concern then stick with
bare-metal, until that software is certified under Xen. However if
your main concern is "getting it to work with maximum performance", go
with SL 4.7

I believe there''s a similar case, where Oracle database is certified
to run under Oracle VM, but NOT under the built-in Xen included in
RHEL or Oracle Enterprise Linux. Even if it runs under RHEL/Xen
there''s no point in doing so if support is a primary concern.

Regards,

Fajar

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It was possible in the early SL4 (4.2 and later  to use older Xen 
kernel tarballs from xen.org Xen 3.0.2 or so, to run a dom0.  I still
have a couple development machines like that.  But it was
never natively built into SL until 4.5 and then it was only for domU.
If you want a SL dom0 then you should be running SL5.2 or 5.3 which
was just released.  DomU support is available for 4.5 and better.

Steve Timm



On Fri, 27 Mar 2009, Ferreira, N. L. (Nuno) wrote:
> Ok.
> So go for a SL 4.7 installation, unless you really need the 4.3 one.
>
> Good luck.
>
> N.
>
> P.S. It is from experience (and talknig with some sysadmins) that you are 
> better off putting a dom0 with a SL OS. Go for a centOS, fedora or RHEL
based
> one, and then build your SL machines on top.
>
> Tim Edwards wrote:
>> Ferreira, N. L. (Nuno) wrote:
>> 
>>> Hi Tim
>>> 
>>> I have a dom0 server running SL 5.1 (i386), and I was able to
install a
>>> SL 4.7 (i386) domU.
>>> When you say virt-install command/libvirt do not allow, what are
the
>>> errors you are getting?
>>> 
>>> Cheers,
>>> N.
>>> 
>> 
>> I''ve looked into the virt-install command in more detail now.
The
>> problem is that the SL4.3 installation tree has no images/xen/
>> directory, whereas more recent RHEL/SL 4.x (eg. 4.6, 4.7) do. The
>> virt-install expects to retrieve a vmlinuz and initrd.img from there.
>> (The error is "Invalid file location given: No such file or
directory")
>> 
>> Tim Edwards
>> 
>> _______________________________________________
>> Xen-users mailing list
>> Xen-users@lists.xensource.com
>> http://lists.xensource.com/xen-users
>> 
>
>
>
-- 
------------------------------------------------------------------
Steven C. Timm, Ph.D  (630) 840-8525
timm@fnal.gov  http://home.fnal.gov/~timm/
Fermilab Computing Division, Scientific Computing Facilities,
Grid Facilities Department, FermiGrid Services Group, Assistant Group Leader.

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