Setting max interrupts per second (WAS printing on firefox)

Oliver Iberien oliver-forward at
Mon Apr 10 05:55:37 UTC 2006

On Saturday 08 April 2006 04:22, Fabian Keil wrote:
> Oliver Iberien <oliver-forward at> wrote:
> > [snip] The printer (Xerox N17, local,
> > parallel port) started cycling through waiting-processing-waiting
> > messages. Rebooting, I saw a message about an IRQ storm on the
> > printer port being "throttled". Killing the job took care of this.
> >
> The default value of hw.intr_storm_threshold is easily reached
> by a printer connected through the parallel port.
> Have a look at: <>.
> Fabian

Thanks for this. Here's the relevent text from that weblog: 

>  As a result, once more harnessed my veteran HP LaserJet 6MP to echunga.
> Printing went at a snail's pace. Finally I discovered the message:
> Interrupt storm detected on "irq7: lpt0"; throttling interrupt source
>  It proved to be a new interrupt throttling feature in the system: the
> sysctl variable hw.intr_storm_threshold sets the maximum number of
> interrupts per second on any interrupt level. The default value is 500,
> woefully inadequate for a PostScript printer on a parallel port, which can
> generate over 100,000 interrupts a second. Fixed that: === root at echunga
> (/dev/ttyp1) ~ 130 -> sysctl hw.intr_storm_threshold  
> hw.intr_storm_threshold: 500 
> === root at echunga (/dev/ttyp1) ~ 131 -> sysctl hw.intr_storm_threshold=200000
> hw.intr_storm_threshold: 500 -> 200000 
>  Unfortunately, this effectively disables the interrupt storm detection
> system-wide. The values should be per interrupt.

Does anyone have any idea what an optimum number would be? 


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