Re: [Xen-users] how to install pv driver for guest os?

[ma qiang <maqiang1984@xxxxxxxxx>]

Hi,

 I am sure I completely followed what http://pastebin.com/fb6fe631 teaches me to do, but sadly, it doesn't seem to work out good. Both the network and disk performance get a little bit worse than before.

I still got some puzzles which I hope you could shed some light on:

(1) the guest os kernel version in http://pastebin.com/fb6fe631 is 2.6.18-128 , while I was doing experiment on CentOS 5.4, whose kernel version is 2.6.18-164. Don't know if this could be a reason why I failed?

(2) I installed the domain0 xen environment by "yum install xen kernel-xen", instead of building from xen source code. So I am wondering is there any domain0 factor that might have affected my result? or is there anything I should do, or at least check on domain0?

Best Wishes!

Qiang Ma

On Sun, Sep 19, 2010 at 6:45 PM, Fajar A. Nugraha <list@xxxxxxxxx> wrote:

On Sun, Sep 19, 2010 at 12:58 PM, ma qiang <maqiang1984@xxxxxxxxx> wrote:
> Thanks for your replies again.
> I have a HVM domU already running. So I have
> tried http://pastebin.com/fb6fe631, and reboot domU successfully. But when I
> run iozone in this domU, I found the performance is worse.

This is a different issue then? Previously you only mention network
throughput problem.

> So I have no idea
> why. I will test the network IO later.

First, make sure that the PV drivers is indeed active, as shown from that link.

# ls -la /sys/class/net/eth0/device
lrwxrwxrwx 1 root root 0 Apr 25 11:50 /sys/class/net/eth0/device ->
../../../devices/xen/vif-0
# ls -la /sys/block/hda/device
lrwxrwxrwx 1 root root 0 Apr 25 11:50 /sys/block/hda/device ->
../../devices/xen/vbd-768

Obviously adjust the device names according to your setup (e.g. you
might have hda1, sda1, or xvda instead of hda). If the output is not
similar, then something's wrong.

After that, check your domU setup. IIRC it's quite "normal" to have
higher performance on domU compared to dom0 when you're using
file-backed domUs (i.e. domU's disk is located as a file on dom0).
This is due to caching effect, and does not show real performance. You
should either use LVM (or partition, or some other block-device), or
use "tap:aio:/" instead of "file:/" on domU config file.

Next, try the same benchmark on dom0. It's normal to have

dom0 throughput >= PV domU throughput > HVM with PV drivers > HVM
without PV drivers.

--
Fajar

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