[Xen-users] How to detect a domain shutdown with as less overhead as possible?

[Lionel Bouton <lionel-subscription@xxxxxxxxxxx>]

Hi,

I've just finished a simple Perl script that brings out a whole domain
from a directory (with a small config file and some <device>.gz files),
create Logical Volumes with each device, starts the domain, wait for the
domain to shutdown, push back into the *.gz the content of the LVs and
remove them. This is quite handy to launch any test machine stored on
the NFS server on one of our Xenified hosts.

My problem is the overhead of checking for the domain to shut down as I
intend to use the domUs not only for functional testing but also to have
a good guess of the performance we can get on real hardware (with only
one domU / real host).

After xm create, this script regularly calls :
xm domid "domainname"
The problem is that this check eats a small chunk of CPU time: it takes
0.2 - 0.3s of real CPU time on each call. I've looked into /proc/xen
hoping to find the list of domains stored here, allowing a simple file
read or stat to give me the information I need, but it seems there's
nothing like this.

Is there a more efficient way of checking if a domain is up?

Note: python is eating CPU in the background on domain-0 for xend when
one domU is up.  It's not a big deal (0.7-1.3% on a PIV 1.6GHz) but I
wonder what xend is doing?

Note : I use Xen-2.0.5 with the packaged 2.4.29-domU and a recompiled
2.6.10-dom0 on Fedora Core 3 hosts.

Lionel.

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