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Date: Thu, 25 Oct 2012 16:13:11 -0200
From: Marcelo Tosatti <mtosatti@redhat.com>
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Subject: Re: [Qemu-devel] [patch v4 00/16] push mmio dispatch out of big lock
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Liu Ping Fan <pingfank@linux.vnet.ibm.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, Avi Kivity <avi@redhat.com>, Anthony Liguori <anthony@codemonkey.ws>, Jan Kiszka <jan.kiszka@siemens.com>, Paolo Bonzini <pbonzini@redhat.com>

On Thu, Oct 25, 2012 at 06:13:51PM +0100, Peter Maydell wrote:
> On 25 October 2012 18:07, Avi Kivity <avi@redhat.com> wrote:
> > On 10/25/2012 04:04 PM, Peter Maydell wrote:
> >> Is there a clear up to date description somewhere of the design and
> >> locking strategy here somewhere? I'd rather not have to try to
> >> reconstitute it by reading the whole patchset...
> >
> > It was described somewhere in a document by Marcelo and myself.
> > Basically the goal is to arrive at
> >
> > address_space_write():
> >   rcu_read_lock()
> >   mr = lookup()
> >   mr->ref()
> >   rcu_read_unlock()
> >
> >   mr->dispatch()
> >
> >   mr->unref()
> >
> > This is the same strategy used in many places in the kernel.
> 
> Yes, but this is rather short on the details (eg, does every
> device have its own lock, what are we doing with irqs, how about
> dma from devices, etc etc). It's the details of the design I'd
> like to see described...
> 
> -- PMM

A document should be maintained and updated to reflect ongoing 
agreement of problems and solutions... Jan/Liu, someone steps up
to do that?

The original is:
http://lists.gnu.org/archive/html/qemu-devel/2012-06/msg04315.html

For one thing, inter-device DMA issue discussed on the list is not
covered and probably large parts of it are obsolete by now (and 
should be deleted).