Subject: Re: freezes with NetBSD 3.99.3 / Xen 2.0.5
To: Malcolm Herbert <>
From: Manuel Bouyer <>
List: current-users
Date: 05/12/2005 20:48:28
On Thu, May 12, 2005 at 09:42:29AM +1000, Malcolm Herbert wrote:
> Not sure whether this is a Xen issue or something to do with -current, 
> hence the cross posting ...
> I have put together a box running NetBSD/Xen with Xen kernel 2.0.5 and 
> NetBSD 3.99.3.
> After some initial problems getting the machine to boot with grub it 
> seems to be mostly fine.  Unfortunately the machine appears to freeze 
> completely for a few seconds every ten minutes or so.  On monitoring 
> the console I have noticed the external USB keyboard detach and 
> reattach, although the freezes still occur with it unplugged.
> Also, it seems that the system clock is running slow - by almost 40 
> minutes after three days and root in domain0 doesn't seem to be able to 
> change it with date or ntpd.  Thirdly, whenever there is a lot of 
> serial port activity (even at 9600bd) the machine seems to slow down 
> markedly - I haven't done any major testing on this, but I have noticed 
> that a networked mp3 stream from the machine to my hardware mp3 player 
> begins to get very very choppy at the same time ...
> Has anyone else noticed these problems with a setup like this?

Well, no. I have a Xen system with an UPS connected to the serial console.
The monitoring daemon talks to the UPS periodically and I never noticed
any slowdown. I don't use USB on this box, though.
Also, ntpd doesn't have problems on this box:
mooney:/home/hera1/permanents/bouyer>ntpq -c peer
     remote           refid      st t when poll reach   delay   offset  jitter
*olympe-61-0   2 u   42   64  376    0.257    3.604   0.111
+routeur-ipv6   2 u   59   64  376    0.254    2.797   0.123

what does 'systat vm' shows when this happens, especially the interrupts
states ? You'll probably want a display highter than 24 rows to have all
interrupt sources displayed.

> Also, I've configured grub to use the PC console to display the menu 
> and use the serial console as the console for the domain0 NetBSD 
> instance.  As I use screen on the serial console I keep invoking Xen 
> kernel's attention string accidentally as it uses three ^A in a row ... 
> is there any way to tell Xen to use some other string, say ^T or 
> something else?

Not that I know. I'd like to change it as well, as tip will trap ^A

> Or perhaps tell Xen to ignore the serial console 
> altogether and just use the PC console?

If you have a serial console I strongly suggest that you keep Xen under
serial console too. sending a R to Xen is usefull on occasions :)
And before doing this, send a 'q' to get enouth debug infos if the
NetBSD domain0 is dead.

Manuel Bouyer <>
     NetBSD: 26 ans d'experience feront toujours la difference