Bad performance Xen Virtual Machine

Thu Jul 31 17:03:11 CDT 2008

Hi,

I am getting a really bad performance out of an Xen installation based on
Ubuntu 8.0.4. I am doing pretty simple tests by the way.

Machine is a brand new PE2950, 16 Gig of mem, 6 x SAS 146 Gig in a raid 10
setup, Perc 6/i controller and 2 x Quad Core Xeon E5420 (2.5GHz, 2x6MB,
1333MHz FSB). Which is a setup recommended by my tech consultant for running
a couple of Xen virtual machines.

OS is as said Ubuntu on an lvm partition on that 6 disk raid 10 setup. Host
is a plain install of Ubuntu + apt-get update / upgrade

I am using 2 test methods for the host, and just one for the guest.

First of all the tool postmark for some disk performance testing.

Without the Xen kernel:

root at vimmerby:/bla# postmark
PostMark v1.51 : 8/14/01
pm>set number 2000
pm>set transactions 5000
pm>set size 500 10000000
pm>set buffering false
pm>run
Creating files...Done
Performing transactions..........Done
Deleting files...Done
Time:
        178 seconds total
        120 seconds of transactions (41 per second)

Files:
        4467 created (25 per second)
                Creation alone: 2000 files (36 per second)
                Mixed with transactions: 2467 files (20 per second)
        2458 read (20 per second)
        2542 appended (21 per second)
        4467 deleted (25 per second)
                Deletion alone: 1934 files (644 per second)
                Mixed with transactions: 2533 files (21 per second)

Data:
        13565.77 megabytes read (76.21 megabytes per second)
        25949.83 megabytes written (145.79 megabytes per second)
pm>set transactions 10000
pm>run
Creating files...Done
Performing transactions..........Done
Deleting files...Done
Time:
        286 seconds total
        233 seconds of transactions (42 per second)

Files:
        6997 created (24 per second)
                Creation alone: 2000 files (40 per second)
                Mixed with transactions: 4997 files (21 per second)
        5021 read (21 per second)
        4979 appended (21 per second)
        6997 deleted (24 per second)
                Deletion alone: 1994 files (498 per second)
                Mixed with transactions: 5003 files (21 per second)

Data:
        29538.12 megabytes read (103.28 megabytes per second)
        42379.89 megabytes written (148.18 megabytes per second)
pm>quit
root at vimmerby:/bla# uname -a
Linux vimmerby 2.6.24-19-server #1 SMP Fri Jul 11 21:50:43 UTC 2008 x86_64
GNU/Linux

With the Xen kernel:

pm>run
Creating files...Done
Performing transactions..........Done
Deleting files...Done
Time:
        273 seconds total
        186 seconds of transactions (26 per second)

Files:
        4467 created (16 per second)
                Creation alone: 2000 files (23 per second)
                Mixed with transactions: 2467 files (13 per second)
        2458 read (13 per second)
        2542 appended (13 per second)
        4467 deleted (16 per second)
                Deletion alone: 1934 files (644 per second)
                Mixed with transactions: 2533 files (13 per second)

Data:
        13565.77 megabytes read (49.69 megabytes per second)
        25949.83 megabytes written (95.05 megabytes per second)
pm>set transactions 10000
pm>run
Creating files...Done
Performing transactions..
Deleting files...Done
Time:
        452 seconds total
        370 seconds of transactions (27 per second)

Files:
        6997 created (15 per second)
                Creation alone: 2000 files (25 per second)
                Mixed with transactions: 4997 files (13 per second)
        5021 read (13 per second)
        4979 appended (13 per second)
        6997 deleted (15 per second)
                Deletion alone: 1994 files (664 per second)
                Mixed with transactions: 5003 files (13 per second)

Data:
        29538.12 megabytes read (65.35 megabytes per second)
        42379.89 megabytes written (93.76 megabytes per second)

Linux vimmerby 2.6.24-19-xen #1 SMP Sat Jul 12 00:15:59 UTC 2008 x86_64
GNU/Linux

Aka the Xen kernel alone gives me a large performance hit it seems.

Now the virtual machines are created on an lvm group:

xen-create-image --partitions standard --hostname vps01
--ip=192.168.1.102--netmask=
255.255.255.0 --gateway=192.168.1.254 --force --memory=1Gb
--install-method=debootstrap --dist=hardy --passwd --lvm=Vimmerby --mirror=
http://se.archive.ubuntu.com/ubuntu/

This is a plain install of a guest, the only thing I do is run an apt-get
update / upgrade and install the apache2-mpm-worker package + dependencies.

Now when I run an apache benchmark from a different server on both the host
os as a guest os I am getting way different performance results in terms of
requests per second:

I run ab with -n 5000 -c 10 http://192.168.1.101/ so I am testing the small
"It works!" file from the default package

On the host OS I get between 2900-3200 requests per second.
On the guest OS I get around 250 Requests per second.

Now I realize the host is not comparible with the guest as the host has more
cpu's and more memory while the virtual machine only has 1 cpu and 1 gb of
mem. However if I increase the number of vcpu's or memory the performance
does not increase. And with just 1 virtual machine on the hardware running I
would expect it's performance slightly lower than the direct testing of the
hardware. No matter what I do it does not seem to get more than 250 Requests
per sec.

Does anybody know what I am doing wrong or how I could setup Ubuntu with Xen
on my hardware?

I am puzzled so could use a bit of help here :-)

Tnx,
Pascal
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.us.dell.com/pipermail/linux-poweredge/attachments/20080731/95d13227/attachment-0001.htm 