From owner-freebsd-net@FreeBSD.ORG  Wed Nov 23 04:54:53 2005
Return-Path: <owner-freebsd-net@FreeBSD.ORG>
X-Original-To: net@freebsd.org
Delivered-To: freebsd-net@FreeBSD.ORG
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 4C63C16A41F;
	Wed, 23 Nov 2005 04:54:53 +0000 (GMT) (envelope-from jdp@polstra.com)
Received: from blake.polstra.com (blake.polstra.com [64.81.189.66])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 93B9843D5C;
	Wed, 23 Nov 2005 04:54:52 +0000 (GMT) (envelope-from jdp@polstra.com)
Received: from t30.polstra.com (t30.polstra.com [64.81.189.72])
	by blake.polstra.com (8.13.1/8.13.1) with ESMTP id jAN4so4s083855
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK);
	Tue, 22 Nov 2005 20:54:51 -0800 (PST)
	(envelope-from jdp@mail.polstra.com)
Received: from t30.polstra.com (localhost [127.0.0.1])
	by t30.polstra.com (8.12.11/8.12.11) with ESMTP id jAN4soYf000536;
	Tue, 22 Nov 2005 20:54:50 -0800 (PST)
	(envelope-from jdp@t30.polstra.com)
Received: (from jdp@localhost)
	by t30.polstra.com (8.12.11/8.12.11/Submit) id jAN4sn8B000535;
	Tue, 22 Nov 2005 20:54:49 -0800 (PST) (envelope-from jdp)
Message-ID: <XFMail.20051122205449.jdp@polstra.com>
X-Mailer: XFMail 1.5.5 on FreeBSD
X-Priority: 3 (Normal)
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0
In-Reply-To: <20051123030304.GA84202@xor.obsecurity.org>
Date: Tue, 22 Nov 2005 20:54:49 -0800 (PST)
From: John Polstra <jdp@polstra.com>
To: Kris Kennaway <kris@obsecurity.org>
Cc: current@freebsd.org, net@freebsd.org
Subject: RE: em interrupt storm
X-BeenThere: freebsd-net@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Networking and TCP/IP with FreeBSD <freebsd-net.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-net>
List-Post: <mailto:freebsd-net@freebsd.org>
List-Help: <mailto:freebsd-net-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 23 Nov 2005 04:54:53 -0000


On 23-Nov-2005 Kris Kennaway wrote:
> I am seeing the em driver undergoing an interrupt storm whenever the
> amr driver receives interrupts.  In this case I was running newfs on
> the amr array and em0 was not in use:
> 
>    28 root        1 -68 -187     0K     8K CPU1   1   0:32 53.98% irq16: em0
>    36 root        1 -64 -183     0K     8K RUN    1   0:37 27.75% irq24: amr0
> 
># vmstat -i
> interrupt                          total       rate
> irq1: atkbd0                           2          0
> irq4: sio0                           199          1
> irq6: fdc0                            32          0
> irq13: npx0                            1          0
> irq14: ata0                           47          0
> irq15: ata1                          931          5
> irq16: em0                       6321801      37187
> irq24: amr0                        28023        164
> cpu0: timer                       337533       1985
> cpu1: timer                       337285       1984
> Total                            7025854      41328
> 
> When newfs finished (i.e. amr was idle), em0 stopped storming.
> 
> MPTable: <INTEL    SE7520BD22  >

This is the dreaded interrupt aliasing problem that several of us have
experienced with this chipset.  High-numbered interrupts alias down to
interrupts in the range 16..19 (or maybe 16..23), a multiple of 8 less
than the original interupt.

Nobody knows what causes it, and nobody knows how to fix it.

John