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Date: Fri, 23 Mar 2012 10:43:28 +0000
From: Chris Webb <chris@arachsys.com>
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Subject: Re: [Qemu-devel] [PATCH] block: add the support to drain throttled
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To: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Zhi Yong Wu <zwu.kernel@gmail.com>, Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>, qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>

Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> writes:

> On Thu, Mar 22, 2012 at 07:07:52PM +0000, Chris Webb wrote:
> > Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> writes:
> > 
> > > Yesterday I only posted an analysis of the bug but here are some
> > > thoughts on how to move forward.  Throttling itself is not the problem.
> > > We've known that synchronous operations in the vcpu thread are a problem
> > > long before throttling.  This is just another reason to convert device
> > > emulation to use asynchronous interfaces.
> > > 
> > > Here is the list of device models that perform synchronous block I/O:
> > > hw/fdc.c
> > > hw/ide/atapi.c
> > > hw/ide/core.c
> > > hw/nand.c
> > > hw/onenand.c
> > > hw/pflash_cfi01.c
> > > hw/pflash_cfi02.c
> > > hw/sd.c
> > > 
> > > Zhi Hui Li is working on hw/fdc.c and recently sent a patch.
> > > 
> > > I think it's too close to QEMU 1.1 to convert all the remaining devices
> > > and test them properly before the soft-freeze.  But it's probably
> > > possible to convert IDE before the soft-freeze.
> > 
> > IDE is the only of these that would affect us as a typical user of
> > throttling. The others aren't really the kind of devices which you'd be
> > using in a hosting setting in any case.
> 
> Can you check whether your Windows guest has DMA or PIO mode enabled?
> 
> http://msdn.microsoft.com/en-us/windows/hardware/gg463526

Hi. We were producing the IDE assert()s and deadlocks with linux kernels.
Although I believe the same symptoms exist on windows, I haven't actually
tested it myself. Typically they would show up in the 16-bit bootloader
code, even before the 32-bit OS has started.

Cheers,

Chris.