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Re: [Xen-users] any opinions on debian vs. opensuse for Xen?

On 10/17/2010 08:14 AM, Miles Fidelman wrote:
Sam wrote:
On 10/16/2010 01:27 PM, Miles Fidelman wrote:
I've been getting just a little fed up with the state of Xen on Debian
Lenny - there are a couple of known bugs that lead to periodic kernel
panics - but fixes haven't made it into the Lenny distribution. I'm sort
of waiting to see how things shake out with Debian Squeeze, when it
becomes stable, but...

I have been using lenny for over a year now. I had some lockups at
first but I never could tell if it was just on vm that was crashing
and bringing the whole setup down. Since I have done cpu pinning and
better ram management, I haven't had any problems.
Based on the console errors I've seen when I have a kernel panic, and
some of the open bug reports I've seen, I'm guessing that cpu pinning
would solve my immediate problem.

But I'm not sure what an effective configuration would be - my current
environment has 2 CPUs and 5 VMs (dom0 + 4 domUs) per server. Not sure
how to set up the pinning, and I expect there would be a performance
hit. So much easier to let the hypervisor allocate CPUs dynamically - if
it worked right.

Sam... could you say a bit more about the configuration details of what
you're doing re. "cpu pinning and better ram management?"



I am running on a dual 1.6ghz cpu intel atom motherboard so of course this is less than ideal. The atom cpu, even though 2 core, has hyper threading which makes dom0 think it has 4 cpus so you have to do some testing to figure out which cpu's are actually on a separate core. dom0 by default has access to all cores. I only have 2 domU's. One has:

cpus = "1,3"
vcpus = 2
memory = 732

while the other has:
cpus = "0,2"
vcpus = 2
memory = 732

Again, note that even though they were passed 2 cpu's, they are just actually getting one hyperthreaded cpu core. dom0 also additionally gets a set amount of ram at boot time.

From menu.lst:
title Xen 3.2-1-amd64 / Debian GNU/Linux, kernel 2.6.26-2-xen-amd64
root            (hd0,0)
kernel          /xen-3.2-1-amd64.gz dom0_mem=256M
module /vmlinuz-2.6.26-2-xen-amd64 root=/dev/mapper/vg0-xen ro console=tty0
module          /initrd.img-2.6.26-2-xen-amd64

That is not much ram for dom0, but not much is going on there in my set up. / is only taking up 900mb. After 4 months of uptime, it finally started using some swap (a whole 10mb). In the /etc/rc.local of dom0 I passed "xm sched-credit -d Domain-0 -w 512" to give dom0 higher priority over other vm's also.

So in your case I would figure out if any of your domU's are considered "more stable" than the others. Put the domU's that you trust stability wise on on cpu, the others on the other cpu. Of course unless they are all equal or have the same distro, then just just put 2 on one cpu and 2 on the other. dom0 will have access to both cpus. I doubt 2 domU's on the same core would crash at the same time and and use up all the resources. Nothing should be crashing anyway.

I would also go with debian squeeze unless you are having trouble with the debian installer. I normally use the net install disk http://www.debian.org/distrib/netinst and then use aptitude to install the rest of my packages. I don't ever use the preset tasks to install any thing.

The wiki has some tips: http://wiki.debian.org/Xen

To install the domU's use this:

Of course, all of these debian ways I have showed you only involve the console and no gui installers. If you are wanting that, you might have to look else where.


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