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Re: [Xen-users] apparently random lockups

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Subject: Re: [Xen-users] apparently random lockups
From: "Eric S. Johansson" <esj@xxxxxxxxxx>
Date: Fri, 23 Dec 2005 12:43:45 -0500
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Eric S. Johansson wrote:
I'm using xen unstable taken from hg repository a couple of days before 3.0 release (how's that for timing).

I've been struggling with a series of random lockups on a domU I'm using as a mailserver. the initial problems were that any significant activity either on the mail server or the IMAP server would cause the domU to go dead with absolute no information in the log files or console.

now that I've had some sleep, here's a little bit more information. It looked like at all the lockups were focused on one particular domU instance. when I woke up, a different domU instance was "dead". it was not responding to connections over its ethernet interface.

I connected to the console and found I could login. ifconfig showed that the interface was up and had an IP address. But I could not go out to that interface to any other machine. Restarting the virtual machine brought the interface back to life.

I think I'm tripping over a series of bugs and getting confused. Teasing apart my experience, I would say that I hit two bugs definitely and the feeling that there are more can be chalked up to paranoia.

Bug 1: dual mounting an LVM partition creates excessively high load averages in a domU instance. By dual mounting I mean mounting the partition in dom0 as well as one domU instance.

even though the load average climbs within the domU, there is no indication of that load climbing from the outside with xm top.

to reproduce, mount one lvm partition in both dom0 and a domU. run some disk intensive process like a recursive grep on the partition in the domU. Load average should climb within a couple of minutes and was unstoppable by my experience.

bug 2: ethernet interfaces go dead. it only seems to happen on one domU at a time but seems tied to ethernet activity level. You should be able to log in via the console and shut down the domU machine. This is much harder to reproduce but I suspect some form of rapid or intense ethernet activity should trigger it.

I suspect both of these problems are easier to reproduce on a slow machine (i.e. Pentium III 500) like the one I'm using. ;-)


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