Re: XEN 4.0 + 2.6.31.13 pvops kernel : system crashes on starting 155th domU

[John McCullough <jmccullo@cs.ucsd.edu>]

I did a little testing.

With no kernel option:
# dmesg | grep -i nr_irqs
[    0.000000] nr_irqs_gsi: 88
[    0.000000] NR_IRQS:4352 nr_irqs:256

w/nr_irqs=65536:
# dmesg | grep -i nr_irqs
[    0.000000] Command line: root=/dev/sda1 ro quiet console=hvc0 
nr_irqs=65536
[    0.000000] nr_irqs_gsi: 88
[    0.000000] Kernel command line: root=/dev/sda1 ro quiet console=hvc0 
nr_irqs=65536
[    0.000000] NR_IRQS:4352 nr_irqs:256

tweaking the NR_IRQS macro in the kernel will change the NR_IRQS output, 
but unfortunately that doesn't change nr_irqs and I run into the same 
limit (36 domus on a less-beefy dual core machine).

I did find this:
http://blogs.sun.com/fvdl/entry/a_million_vms
which references NR_DYNIRQS, which is in 2.6.18, but not in the pvops 
kernel.

Watching /proc/interrupts, the domain irqs seem to be getting allocated 
from 248 downward until they hit some other limit:
...
  64:      59104  xen-pirq-ioapic-level  ioc0
  89:          1   xen-dyn-event     evtchn:xenconsoled
  90:          1   xen-dyn-event     evtchn:xenstored
  91:          6   xen-dyn-event     vif36.0
  92:        140   xen-dyn-event     blkif-backend
  93:         97   xen-dyn-event     evtchn:xenconsoled
  94:        139   xen-dyn-event     evtchn:xenstored
  95:          7   xen-dyn-event     vif35.0
  96:        301   xen-dyn-event     blkif-backend
  97:        261   xen-dyn-event     evtchn:xenconsoled
  98:        145   xen-dyn-event     evtchn:xenstored
  99:          7   xen-dyn-event     vif34.0
...
Perhaps the xen irqs are getting allocated out of the nr_irqs pool, 
while they could be allocated from the NR_IRQS pool?

-John




On 04/27/2010 08:45 PM, Keir Fraser wrote:
> I think nr_irqs is specifiable on the command line on newer kernels. You may
> be able to do nr_irqs=65536 as a kernel boot parameter, or something like
> that, without needing to rebuild the kernel.
>
>   -- Keir
>
> On 28/04/2010 02:02, "Yuvraj Agarwal"<yuvraj@cs.ucsd.edu>  wrote:
>
>    
>> Actually, I did identify the problem (don’t know the fix) at least from
>> the console logs. Its related to running out of nr_irq's  (attached JPG
>> for the console log).
>>
>>
>> -----Original Message-----
>> From: xen-devel-bounces@lists.xensource.com
>> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Keir Fraser
>> Sent: Tuesday, April 27, 2010 5:44 PM
>> To: Yuvraj Agarwal; xen-devel@lists.xensource.com
>> Subject: Re: [Xen-devel] XEN 4.0 + 2.6.31.13 pvops kernel : system crashes
>> on starting 155th domU
>>
>> On 27/04/2010 08:41, "Yuvraj Agarwal"<yuvraj@cs.ucsd.edu>  wrote:
>>
>>      
>>> Attached is the output of /var/log/daemon.log and /var/log/xen/xend.log,
>>>        
>> but
>>      
>>> as far as we can see we don¹t quite know what might be going causing the
>>> system to crash (no console access anymore and system becomes
>>>        
>> unresponsive and
>>      
>>> needs to be power-cycled).  I have pasted only the relevant bits of
>>> information (the last domU that did successfully start and the next one
>>>        
>> that
>>      
>>> failed). It may be the case that all the log messages weren¹t flushed
>>>        
>> before
>>      
>>> the system crashedŠ
>>>
>>> Does anyone know where this limit of 155 domU is coming from and how we
>>>        
>> can
>>      
>>> fix/increase it?
>>>        
>> Get a serial line on a test box, and capture Xen logging output on it. You
>> can both see if any crash messages come from Xen when the 155th domain is
>> created, and also try the serial debug keys (e.g., try 'h' to get help to
>> start with) to see whether Xen itself is still alive.
>>
>>   -- Keir
>>
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xensource.com
>> http://lists.xensource.com/xen-devel
>>      
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>