Re: [Xen-users] Xen dom0 load affecting domUs

[Peter Viskup <skupko.sk@xxxxxxxxx>]

On 12/04/2012 07:24 PM, Riyan S wrote:

Hello folks,

I have a Xen server running on Centos 6.2 with 3.6.6-1.el6xen.x86_64 as the Dom0 kernel, and i  have dedicted 2 CPUs and 4G ram for the Dom0.I have close to 4-5 Virtual machines running on the Xen server.

The problem is that for some reason,carrying outany CPU/Disk intensive task on the Dom0 seems to be affecting the DomUs adversly.For ex.i noticed that my Domus become extremly sluggish if i use a 'dd' command to create  a 80G file on the Dom0,is this behaviour normal ? I guess,may be i should use a Sparse file instead ?

So if i have more VMs,do i need to allocate more resources for the Dom0 in terms of memory and cpu ? As of now all the VMs use a loopback device in the Dom0 .

The dom0 itself is not much memory or CPU consuming. Therefore 512 or 768MB should be enough for dom0. The most important part for successfully running more domUs on your server is to have good storage design and fast IO subsystem. Some (real) HW RAID controller with cache or FibreChannel or iSCSI over fast Ethernet is something you should think about.
Anyway the behavior you are experiencing is expected and normal. This is usually something the VPS users do not think about - enough memory and CPU doesn't mean your virtual server will run 'fast'. ;-)
I am using 'ionice -c 3' when some intensive IO load is needed to perform on dom0. You can also use the 'nice' command if you wish. (test it with running '/usr/bin/time -v' ;-) )
The other thing you can take care of is to set the scheduler attributes of every domU (via 'xm sched-cred' for example).

--
Peter Viskup

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