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[Xen-users] RE: [Xen-devel] NR_IRQ limit

To: Eric Windisch <eric@xxxxxxxxxxxx>
Subject: [Xen-users] RE: [Xen-devel] NR_IRQ limit
From: "Subrahmanian, Raj" <raj.subrahmanian@xxxxxxxxxx>
Date: Fri, 29 Feb 2008 16:58:34 -0600
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Thread-topic: [Xen-devel] NR_IRQ limit
I don't think that you need to change the NR_VECTORS value in Xen. My 
understanding is that these IRQs are being doled out of Dom0, and not Xen 
Incidentally, we did run 320 VMs here at Unisys. Any reason you are shooting 
for 320 in particular?
Also, as you increase the number of VMs, you will run out of Xen's heap (which 
is set at 10 or 12 MB), soon and then you will need to change that with the 
boot option. We set it at 64 MB, just to be safe.

>-----Original Message-----
>From: Eric Windisch [mailto:eric@xxxxxxxxxxxx]
>Sent: Friday, February 29, 2008 5:52 PM
>To: Subrahmanian, Raj
>Cc: xen-users@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [Xen-devel] NR_IRQ limit
>On Feb 29, 2008, at 5:13 PM, Subrahmanian, Raj wrote:
>> Eric,
>> In that case, you will need to change the NR_DYNIRQS value in ./
>> linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/irq_vectors.h and
>> recompile your Dom0.
>Thank you.  I assume I'll still have to change NR_VECTORS in
>Xen itself, right?
>> I think you are trying to boot large numbers of VMs.
>I'm currently booting 80 guests, each with two vdb, one vif.   I am
>prevented from creating more at this time due to the limited
>number of IRQs (80*3=240 + various others for
>console/xenbus/etc).  Ultimately, I'd like to try bringing
>this up to 160, or even 320 guests if the hardware allows.
>My kernels are compiling now, I'll test them out on my test
>machine, and hopefully I'll be able to get these changes into
>production tomorrow.
>Eric Windisch
>PH: 1-800-630-0476
>IM: support@xxxxxxxxxxxx (jabber/xmpp)
>IM: grokthissupport (AIM)
>IM: grokthisnet (Yahoo)

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