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

[Avi Kivity]

On 07/14/2011 10:14 AM, Umesh Deshpande wrote:
> Following patch is implemented to deal with the VCPU and iothread starvation 
> during the migration of a guest. Currently iothread is responsible for 
> performing the migration. It holds the qemu_mutex during the migration and 
> doesn't allow VCPU to enter the qemu mode and delays its return to the guest. 
> The guest migration, executed as an iohandler also delays the execution of 
> other iohandlers. In the following patch, the migration has been moved to a 
> separate thread to reduce the qemu_mutex contention and iohandler starvation.
>
>
> @@ -260,10 +260,15 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
> void *opaque)
>           return 0;
>       }
>
> +    if (stage != 3)
> +        qemu_mutex_lock_iothread();

Please read CODING_STYLE, especially the bit about braces.

Does this mean that the following code is sometimes executed without 
qemu_mutex?  I don't think any of it is thread safe.

Even just reading memory is not thread safe.  You either have to copy it 
into a buffer under lock, or convert the memory API to RCU.

--
error compiling committee.c: too many arguments to function