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Re: [Xen-users] RHEL6 domU migrate issues w/ higher to lower frequency C

To: Joshua West <jwest@xxxxxxxxxxxx>
Subject: Re: [Xen-users] RHEL6 domU migrate issues w/ higher to lower frequency CPU's
From: Paras pradhan <pradhanparas@xxxxxxxxx>
Date: Thu, 16 Dec 2010 09:40:33 -0600
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
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I am having exactly the same problem. Plus this bug is seen when you
have the same cpu in both nodes too. I have tested in Quad-Core AMD
Opteron(tm) Processor 8374 HE in both nodes and same problem.


* Start the node in node1. No problem
* Live migrate to Node2 (same cpu, 100% same hardware). domU
unresponsive, no output in xm console, can ping ,can see ssh banner
but dead slow
* Migrate back in node1, No problem

I could reproduce this problem in another set of systems too. Same problem.

I have a ticket opened with Redhat from around 2 weeks. no help till now.

Also I have seen this bug filed at Redhat but dunno if they are
working on it or not.

This is really frustrating.


On Wed, Dec 15, 2010 at 5:03 PM, Joshua West <jwest@xxxxxxxxxxxx> wrote:
> Hey folks,
> I've encountered a rather interesting/frustrating issue with RHEL6 domU's
> and live migration.
> I have no problems booting a RHEL6 domU using its stock/native kernel on Xen
> 3.4.1 or Xen 3.4.3.  But in terms of live migration, there seems to be a
> problem when moving from a higher (in terms of CPU MHz) to lower (MHz)
> system -- even if the higher of the two is a much older CPU model.
> For example, I can reproduce the bug under Xen 3.4.3 with the following:
>  * Migrating from X5450 @ 3.00GHz to X5355 @ 2.66GHz fails, but the opposite
> (increasing in CPU frequency) succeeds.
>  * Migrating from Xeon(TM) CPU 2.80GHz to E5310 @ 1.60GHz fails, but the
> opposite (increasing in CPU frequency) succeeds.
> BTW, when I say "fails", what I really mean is the migration succeeds but
> the domU is no longer responsive.  I can attach to the console via 'xm
> console' but nothing is displayed, although occasionally a new line is
> printed as i bang my hands on the Enter key.  Occasionally ping works and
> occasionally I can establish a connection to the domU's port 22 and see the
> OpenSSH banner, but thats as far as I get.  Its not like the domU is runaway
> with 100% cpu.  It sits with state "-b----" (xm list).
> I have tested cpuid masking but this doesn't help.  Its an issue with going
> from a higher CPU frequency system to a lower CPU frequency system.
> This is using the stock RHEL6 kernel 'vmlinuz-2.6.32-71.7.1.el6.x86_64'.
> Anybody have suggestions on the cause or a workaround?  Experience this
> issue too?
> I've heard through the grapevine that this bug is also confirmed with RHEL6
> domU's on XCP 1.0.
> Thanks for any help you can provide!
> --
> Joshua West
> Senior Systems Engineer
> Brandeis University
> http://www.brandeis.edu
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