Re: [Qemu-devel] [RFC] New thread for the VM migration

[Anthony Liguori <anthony@codemonkey.ws>]

On 07/14/2011 07:32 AM, Avi Kivity wrote:
> On 07/14/2011 03:30 PM, Anthony Liguori wrote:
>>> Does this mean that the following code is sometimes executed without
>>> qemu_mutex? I don't think any of it is thread safe.
>>
>>
>> That was my reaction too.
>>
>> I think the most rational thing to do is have a separate thread and a
>> pair of producer/consumer queues.
>>
>> The I/O thread can push virtual addresses and sizes to the queue for
>> the migration thread to compress/write() to the fd. The migration
>> thread can then push sent regions onto a separate queue for the I/O
>> thread to mark as dirty.
>
> Even virtual addresses are not safe enough, because of hotunplug.
> Without some kind of locking, you have to copy the data.

We don't know yet how we're going to implement hot unplug so let's not 
worry about this for now.

I think a reference count based approach is really the only sane thing 
to do and if we did that, it wouldn't be a problem since the reference 
would be owned by the I/O thread and would live until the migration 
thread is done with the VA.

Regards,

Anthony Liguori

>