Re: [Qemu-devel] [PATCH V3 10/11] vcpu: introduce lockmap

[Avi Kivity]

On 09/11/2012 01:04 PM, Jan Kiszka wrote:

>> DMA is inherently asynchronous, so we already drop the lock between
>> initiation and completion; we need to find a way to make it easy to use
>> the API without taking the lock while the transfer takes place.
> 
> We will have to review/rework device models that want to use the new
> locking scheme in a way that they can drop their own lock while issuing
> DMA. But that is surely non-trivial.

Most DMA today happens without the big qemu lock.  We only need to
convert the paths that actually access memory, these are the block and
network layers (for the respective devices).

> The other option is to keep DMA requests issued by devices synchronous
> but let them fail if we are about to lock up. Still requires changes,
> but is probably more comprehensible for device model developers.

How do you handle failures?

-- 
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