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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Apr 27, 2010 at 11:47:30PM -0700, John McCullough wrote:
> 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).

If you have CONFIG_SPARSE_IRQ defined in your .config, it gets
overwritten by some code that figures out how many IRQs you need based
on your CPU count.

So can you change NR_VECTORS in arch/x86/include/asm/irq_vectors.h to a
higher value and see what happens?

>
> 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:

Yeah. They hit the nr_irqs_gsi and don't go below that.

> ...
>  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
>>>      
>>
>>
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>>    
>
>
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