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RE: [Xen-devel] Maximum number of domains and NR_IRQS

  • To: "Keir Fraser" <keir@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Carb, Brian A" <Brian.Carb@xxxxxxxxxx>
  • Date: Thu, 7 Dec 2006 11:08:30 -0500
  • Delivery-date: Thu, 07 Dec 2006 08:08:39 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AccaFYwFy8r1fHrHTUe4UDnJ0i4NHgAAeZuMAAA6YpA=
  • Thread-topic: [Xen-devel] Maximum number of domains and NR_IRQS

We changed NR_IRQS in xen-unstable.hg/linux- - it's set to 224 by default.

brian carb
unisys corporation - malvern, pa


From: Keir Fraser [mailto:keir@xxxxxxxxxxxxx]
Sent: Thursday, December 07, 2006 10:51 AM
To: Carb, Brian A; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Maximum number of domains and NR_IRQS

On 7/12/06 15:37, "Carb, Brian A" <Brian.Carb@xxxxxxxxxx> wrote:

We successfully start 118 DOMUs, but when we try to start the 119th, the system panics with the following messages:
  Kernel panic - not syncing: No available IRQ to bind to: increase NR_IRQS!
  (XEN) Domain 0 crashed: rebooting machine in 5 seconds.

The documentation in include/asm-x86_64/irq.h suggests that the value of NR_IRQS under x86_64 is limited to 256. In fact, when we rebuilt xen-unstable with NR_IRQS set to 768, the kernel panics on boot (see below).

It’s not Xen’s NR_IRQS you should increase; only Linux’s.

This out-of-IRQs condition shouldn’t crash the dom0 of course. I’ll look into that.

 -- Keir
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