* [Qemu-devel] scheduling of qemu threads
@ 2008-07-31 15:50 David S. Ahern
2008-07-31 16:02 ` [Qemu-devel] " Anthony Liguori
0 siblings, 1 reply; 3+ messages in thread
From: David S. Ahern @ 2008-07-31 15:50 UTC (permalink / raw)
To: Anthony Liguori, qemu-devel
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?
david
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Qemu-devel] Re: scheduling of qemu threads
2008-07-31 15:50 [Qemu-devel] scheduling of qemu threads David S. Ahern
@ 2008-07-31 16:02 ` Anthony Liguori
2008-08-01 11:50 ` David S. Ahern
0 siblings, 1 reply; 3+ messages in thread
From: Anthony Liguori @ 2008-07-31 16:02 UTC (permalink / raw)
To: David S. Ahern; +Cc: qemu-devel
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.
Regards,
Anthony Liguori
> david
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Qemu-devel] Re: scheduling of qemu threads
2008-07-31 16:02 ` [Qemu-devel] " Anthony Liguori
@ 2008-08-01 11:50 ` David S. Ahern
0 siblings, 0 replies; 3+ messages in thread
From: David S. Ahern @ 2008-08-01 11:50 UTC (permalink / raw)
To: Anthony Liguori; +Cc: qemu-devel
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
>>
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2008-07-31 15:50 [Qemu-devel] scheduling of qemu threads David S. Ahern
2008-07-31 16:02 ` [Qemu-devel] " Anthony Liguori
2008-08-01 11:50 ` David S. Ahern
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