[Qemu-devel] Re: scheduling of qemu threads

[David S. Ahern]

Anthony Liguori wrote:
> David S. Ahern wrote:
>> Last week or so Anthony made a comment about qemu basically being single
>> threaded given its global mutex. What are the impacts to simultaneous
>> scheduling of qemu threads? As I understand it, qemu has a main thread,
>> a monitor thread, an IO thread and a thread for each vcpu. Can 2 or more
>> vcpu threads run concurrently? Can a vcpu thread and an IO thread run
>> concurrently? Does kvm alter the concurrency?
>>   
> 
> All threads run in lock-step except when a VCPU is running (via
> kvm_run).  So a VCPU can run while the IO thread is active.  Only one
> VCPU can execute IO at a given time though.

Not to be dense, but do you mean yes 2 or more vcpu threads can be run
at the same time? I ask because it does not make sense for them not to
be performance wise, but at the same time following the code from
kvm_main_loop_cpu() to kvm_run() I do not see the qemu_mutex unlocked
before the ioctl(). I only see it unlocked in kvm_main_loop_wait().

thanks,
david

> 
> Regards,
> 
> Anthony Liguori
> 
>> david
>>   
> 
>