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@xxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx
>>> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir Fraser
>>> Sent: Tuesday, April 27, 2010 5:44 PM
>>> To: Yuvraj Agarwal; xen-devel@xxxxxxxxxxxxxxxxxxx
>>> 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@xxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx
>>> http://lists.xensource.com/xen-devel
>>>
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
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>> http://lists.xensource.com/xen-devel
>>
>
>
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