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Date: Thu, 25 Oct 2012 18:13:51 +0100
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From: Peter Maydell <peter.maydell@linaro.org>
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Subject: Re: [Qemu-devel] [patch v4 00/16] push mmio dispatch out of big lock
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To: Avi Kivity <avi@redhat.com>
Cc: Liu Ping Fan <pingfank@linux.vnet.ibm.com>, Stefan Hajnoczi <stefanha@gmail.com>, Marcelo Tosatti <mtosatti@redhat.com>, qemu-devel@nongnu.org, Anthony Liguori <anthony@codemonkey.ws>, Jan Kiszka <jan.kiszka@siemens.com>, Paolo Bonzini <pbonzini@redhat.com>

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