Interrupt storm on ahc0 when drm module is loaded

[Gary Jennejohn]

On Wed, 26 Sep 2007 12:36:44 +0100
bruce at cran.org.uk wrote:

> I've come some sort of conflict between the drm and ahc drivers:
> whenever drm is loaded I get an interrupt storm on ahc0.  My system is:
> 
> 7.0-CURRENT #0: Tue Sep 25 18:08:50 BST 2007
> /usr/obj/usr/src/sys/GENERIC i386
> 
> I'm running Xorg 7.3
> 
> ahc0: <Adaptec 19160B Ultra160 SCSI adapter> port 0xdc00-0xdcff mem
> 0xd9200000-0xd9200fff irq 16 at device 9.0 on pci0
> ahc0: [ITHREAD]
> da0 at ahc0 bus 0 target 6 lun 0
> 
> drm0: <Matrox G200 (AGP)> on vgapci0
> info: [drm] AGP at 0xd0000000 64MB
> info: [drm] Initialized mga 3.2.2 20060319
> info: [drm] Initialized card for AGP DMA
> drm0: [ITHREAD]
> 
> vmstat -i:
> interrupt	total		rate
> irq1: atkbd0	4036		0
> irq14: ata0	58		0
> irq16: ahc0	15004943	2824
> irq19: fxp0	40961		7
> cpu0: timer	10624196	1999
> cpu1: timer	10606936	1996
> Total		36281130	6828
> 
> Over time the rate for ahc0 grows until I get the "Interrupt storm
> detected: throttling irq16" messages. I can trigger the problem by
> changing the default colour depth to 16 bits in my xorg.conf file: this
> enables the drm module to load and immediately the interrupt rate starts
> to climb.
> 

Have you looked at disabling interrupts for VGA in your BIOS (if
possible)? Don't know what effect this would have on X11's performance.

You could also try a different PCI slot.

An unrelated question. I also have a 19160 but the SCSI BIOS never shows up at
boot time so I can't boot from it. Did you ever see anything like that?

-- 
Gary Jennejohn