From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:54502)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1SB2j8-0001D6-Nn
	for qemu-devel@nongnu.org; Fri, 23 Mar 2012 07:32:18 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1SB2j2-0000fU-F9
	for qemu-devel@nongnu.org; Fri, 23 Mar 2012 07:32:14 -0400
Received: from mail-lb0-f173.google.com ([209.85.217.173]:49268)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1SB2j2-0000ds-20
	for qemu-devel@nongnu.org; Fri, 23 Mar 2012 07:32:08 -0400
Received: by lbon3 with SMTP id n3so2422609lbo.4
	for <qemu-devel@nongnu.org>; Fri, 23 Mar 2012 04:32:05 -0700 (PDT)
MIME-Version: 1.0
In-Reply-To: <20120323110230.GK17656@alpha.arachsys.com>
References: <1331603611-9103-1-git-send-email-zwu.kernel@gmail.com>
	<CAEH94LhwKWyg8pVTY7-SeB68eBRY-1-tDQ=Z=pXtH2_amr4jFw@mail.gmail.com>
	<4F685230.9040209@redhat.com> <4F6854B2.8000209@redhat.com>
	<20120320114442.GA30819@stefanha-thinkpad.localdomain>
	<20120322190751.GA12145@arachsys.com>
	<20120323103814.GA21835@stefanha-thinkpad.localdomain>
	<20120323104327.GE19671@arachsys.com>
	<CAJSP0QW7FzX425ExBn7Ug4TCHXBfhsB-onqP3PDMz_JvtSsX0g@mail.gmail.com>
	<20120323110230.GK17656@alpha.arachsys.com>
Date: Fri, 23 Mar 2012 11:32:05 +0000
Message-ID: <CAJSP0QXpaybc7zhQJ8T0vaY1ktu5-odZNwCNamj-rvzQUJQDZQ@mail.gmail.com>
From: Stefan Hajnoczi <stefanha@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Subject: Re: [Qemu-devel] [PATCH] block: add the support to drain throttled
	requests
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Richard Davies <richard@arachsys.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Chris Webb <chris@arachsys.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, qemu-devel@nongnu.org, Zhi Yong Wu <zwu.kernel@gmail.com>, Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>, Paolo Bonzini <pbonzini@redhat.com>

On Fri, Mar 23, 2012 at 11:02 AM, Richard Davies <richard@arachsys.com> wro=
te:
> Stefan Hajnoczi wrote:
>> > Hi. We were producing the IDE assert()s and deadlocks with linux kerne=
ls.
>> > Although I believe the same symptoms exist on windows, I haven't actua=
lly
>> > tested it myself. Typically they would show up in the 16-bit bootloade=
r
>> > code, even before the 32-bit OS has started.
>>
>> Okay, that makes sense. =A0Bootloaders and the BIOS may use the simplest
>> driver interface - which may be PIO in the case. =A0I asked because the
>> IDE DMA code path should work with I/O throttling and Windows is known
>> for sometimes falling back to the PIO code path when some heuristics
>> trigger.
>
> Whilst the bootloader was the easiest place for us to replicate this
> deadlock, we have also seen it with running Linux VMs.
>
> Older Linux kernels (e.g. CentOS 5) will fall back to PIO mode on IDE
> devices if they experience storage timeouts (e.g. due to heavy contention=
 of
> underlying storage from other VMs).
>
> Hence, the IO limits deadlock can lead to running Linux VMs locking up as
> well as just Windows and Linux bootloaders.

Thanks for pointing out that Linux falls back too.

Stefan