Comments for Slow Xen virtualization of RHEL 3 i386 guest on RHEL 5 x86_64

[phinjensen]

Comments for https://www.endpointdev.com/blog/2009/01/slow-xen-virtualization-of-rhel-3-i386/
By Jon Jensen

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[phinjensen]

original author: kabewm
date: 2009-01-28T01:54:00-05:00

You can try using the paravirt kernel from xen.org

http://www.xen.org/download/index_3.0.3.html

[phinjensen]

original author: laclasse
date: 2009-01-30T19:17:00-05:00

Immediate guesses are degradated I/O performance on the guest due to using file-backed disk storage (tap:io).

If this is the case, much better performance can be archieved buy creating the new LV on a dom0 VG, and pointing the new lv to the VM.

Did you contact support?

[phinjensen]

original author: Donald
date: 2009-02-26T13:53:00-05:00

Without pv drivers in the guest, FV guests exhibit poor block & net performance, and can use significant host resources (in qemu-dm) to trap & emulate the FV IO devices (realtek nic, ide disk).

So, the solution for all FV guests (be it Linux or Windows) is to provide & install pv drivers for nic & block.

For rhel3, RH provides the kmod-xenpv pkg as mentioned in this articles. To use it:

First, ensure you are running rhel3-u9.

second, make sure your (xen) guest config file has type=ioemu removed from your (nic) config after you have installed the xen pv drivers.
Note: the driver's don't autoload under rhel3, so ensure you follow the doc instructions to ensure the drivers are loaded on boot.

Note, also, that you can't use the vbd
driver for boot disk (unless you rebuild initrd & set ide=disable), so you want to split
your applic. disk/partition from boot disk/partition/image, and configure the
applic disk/partition/image to xvdb
(but <= xvdg).

We (RedHat) just tested the above,
rhel3-u9-i386 + vnif + vbd on rhel5.3 x86_64 host and it all worked.

The documentation about rhel3 i386 guests not working on x86_64 rhel5 hosts is incorrect. We will rev that document to eliminate that confusion.

[phinjensen]

original author: Jon Jensen
date: 2009-02-26T16:31:00-05:00

Donald, thanks for your update. We'll give it a shot. For the VM of most interest we'll have to do some surgery since it's one large disk for boot + app and data.

I appreciate your reply.