From owner-freebsd-current@FreeBSD.ORG  Wed Sep 26 11:36:46 2007
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: current@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 1F5CE16A41B
	for <current@freebsd.org>; Wed, 26 Sep 2007 11:36:46 +0000 (UTC)
	(envelope-from brucec@muon.bluestop.org)
Received: from muon.bluestop.org (muon.bluestop.org [80.68.94.188])
	by mx1.freebsd.org (Postfix) with ESMTP id 060F113C448
	for <current@freebsd.org>; Wed, 26 Sep 2007 11:36:45 +0000 (UTC)
	(envelope-from brucec@muon.bluestop.org)
Received: by muon.bluestop.org (Postfix, from userid 1000)
	id 3F69A301F6; Wed, 26 Sep 2007 12:36:44 +0100 (BST)
Date: Wed, 26 Sep 2007 12:36:44 +0100
From: bruce@cran.org.uk
To: current@freebsd.org
Message-ID: <20070926113643.GA21109@muon.bluestop.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.5.13 (2006-08-11)
Cc: 
Subject: Interrupt storm on ahc0 when drm module is loaded
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>, 
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 26 Sep 2007 11:36:46 -0000

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.

--
Bruce