Part II: Running SMP kernel but only one cpu

Tim Judd tajudd at
Tue May 5 03:45:48 UTC 2009

On Mon, May 4, 2009 at 6:46 PM, Duane <duane at> wrote:

> The bios in this old Micron dual PPro-180 full tower antique only
> initializes the second CPU if the machine is cold-booted.  A simple
> 'reboot' results in a single processor machine regardless of the
> kernel that is launched. This fact -- unknown to me before last night
> -- was the source of a great deal of lost time!
> My 6.4 SMP kernel (now customized) runs just fine, with both cpus
> active, *except* for this message streaming constantly up the boot
> console.
> (from /var/log/messages:)
> May  4 20:20:33 poobah kernel: interrupt storm detected on "irq15:";
> throttling interrupt source
> May  4 20:21:02 poobah last message repeated 42 times
> May  4 20:21:03 poobah login: ROOT LOGIN (root) ON ttyv1
> May  4 20:21:03 poobah kernel: interrupt storm detected on "irq15:";
> throttling interrupt source
> May  4 20:21:33 poobah last message repeated 30 times
> May  4 20:23:33 poobah last message repeated 120 times
> May  4 20:33:33 poobah last message repeated 599 times
> May  4 20:40:01 poobah last message repeated 387 times
> etc etc ad repetitum infinitum
> Question1: Is this something I should go to some lengths to eliminate?
> Question2: What the heck is it?
> Best regards,
> --
> Duane

IRQ15 is typically your secondary IDE controller; but due to PCI (or E-ISA)
plug&play, including the PnP the BIOS may setup, lots of others can be on
that bus too.

Likely candidates are PCI devices, such as modems, NICs, sound cards, etc

I think you'd be able to find what's on IRQ15 by a simple:
  # grep -i irq15 /var/run/dmesg.boot

You will probably not be able to pull your secondary IDE controller off 15.
The possible other device that's been configured for irq15 might stop if you
disable PnP OS in the BIOS (if it exists), or setting irq15 to the
equivelant of 'reserved' in the BIOS might aleviate the problem.

Good luck.

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