Re: [Qemu-devel] [patch v4 00/16] push mmio dispatch out of big lock

[Jan Kiszka]

On 2012-10-25 20:13, Marcelo Tosatti wrote:
> On Thu, Oct 25, 2012 at 06:13:51PM +0100, Peter Maydell wrote:
>> On 25 October 2012 18:07, Avi Kivity <address@hidden> 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?

I can pick this up as I have to anyway. First results will be pushed to
the wiki, around or after the KVM forum.

Jan

> 
> 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).

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