xm sched-credit2 - changing weight of dom0 freezes machine

xm sched-credit2 - changing weight of dom0 freezes machine

[John Weekes]

In testing credit2, I have observed that changing the weight of dom0 
freezes a machine on RELEASE-4.1.0. Executing this command immediately 
causes a freeze, for instance:

xm sched-credit2 -d 0 -w 256

This is with the latest stable-2.6.32 (2.6.32.35-gdf3a556). I haven't 
tested with credit2 previously, so I don't know how long this problem 
has existed.

I also saw a different freeze event after starting up 20 or so domains 
on one machine. There were no messages in the xend.log or 
/var/log/messages after the freeze -- the machine just stopped 
responding, as it does when trying to change the dom0 weight. How can I 
effectively debug this if I see it happen again?

-John

Re: xm sched-credit2 - changing weight of dom0 freezes machine

[Pasi Kärkkäinen]

On Mon, Mar 28, 2011 at 12:30:08AM -0700, John Weekes wrote:
> In testing credit2, I have observed that changing the weight of dom0  
> freezes a machine on RELEASE-4.1.0. Executing this command immediately  
> causes a freeze, for instance:
>
> xm sched-credit2 -d 0 -w 256
>

Ouch. Any output at all on the console?

> This is with the latest stable-2.6.32 (2.6.32.35-gdf3a556). I haven't  
> tested with credit2 previously, so I don't know how long this problem  
> has existed.
>
> I also saw a different freeze event after starting up 20 or so domains  
> on one machine. There were no messages in the xend.log or  
> /var/log/messages after the freeze -- the machine just stopped  
> responding, as it does when trying to change the dom0 weight. How can I  
> effectively debug this if I see it happen again?
>

You should set up a serial console and enable various debugging/logging options..

Serial console: http://wiki.xensource.com/xenwiki/XenSerialConsole
Various debugging options for dom0 kernel: http://wiki.xen.org/xenwiki/XenParavirtOps

-- Pasi