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Re: [Xen-users] maximum number of domus with xen 3.2

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Subject: Re: [Xen-users] maximum number of domus with xen 3.2
From: Markus Hochholdinger <Markus@xxxxxxxxxxxxxxxxx>
Date: Fri, 21 Aug 2009 19:58:23 +0200
Cc: Yuvraj Agarwal <yuvraj.agarwal@xxxxxxxxx>
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Hi Yuvraj,

Am 21.08.2009 um 19:34 Uhr schrieb Yuvraj Agarwal <yuvraj.agarwal@xxxxxxxxx>:
> I saw your message on the XEN mailing list. I am also trying to test a
> setup where I want to instantiate a large number of VMs on a single
> physical box.
> I am running Ubuntu 8.04 Server (64bit), with Xen 3.2.
> I was wondering if you ever got an answer about the limit on the

yes. I had to increase NR_DYNIRQS in my dom0 kernel. To increase NR_DYNIRQS 
you have to (re-)compile your dom0 kernel. With this I was able to start more 
domUs on one dom0.

> number of domUs you can instantiate on XEN 3.2 ?  I have not yet
> started up a large number of VMs, but for my experimentation I would
> like to have several hundreds of domUs. I have enough memory in this
> system and each domU is of a very small footprint.
> I do have the lop max_loop=256 (that is the maximum I believe).
> Any advice, help is appreciated! Seems like you were essentially
> trying something similar on a similar software (Xen 3.2) setup....

For every block device and every network device you assign to your domUs you 
loose one DYNIRQS in your dom0. If you hit the limit you will get a kernel 
message like:
  "No available IRQ to bind to: increase NR_DYNIRQS."



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