Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests

[Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>]

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

Stefan