Re: [PATCH] qemu-kvm/rbd: add queueing delay based on queuesize (using use qemu_mutex_* and qemu_cond_*)

[Kevin Wolf <kwolf@redhat.com>]

Am 21.07.2010 21:18, schrieb Christian Brunner:
> 2010/7/20 Yehuda Sadeh Weinraub <yehudasa@gmail.com>:
>>> +        while  (s->queuesize > MAX_QUEUE_SIZE) {
>>> +            qemu_mutex_lock(s->queue_mutex);
>>> +            qemu_cond_wait(s->queue_threshold, s->queue_mutex);
>>> +            qemu_mutex_unlock(s->queue_mutex);
>>> +        }
>>
>> Actually we shouldn't be waiting inside the aio handler. We should
>> probably be feeding the request into some wait queue and have a
>> separate thread that drains all those requests out. Though this
>> wouldn't help us in throttling the client memory, it's probably a more
>> correct way to handle the problem.
> 
> I agree with you, however I don't think that this is worth the effort.
> I've never seen this occur when running a virtual machine, only when
> running qemu-io.
> 
> @Kevin: Did you follow this thread? What is your opinion?

No, I'm not subscribed to your mailing list and qemu-devel isn't CCed.

I'm not entirely sure what kind of queue this is about, but are you sure
that it can only happen with large requests as issued by qemu-io? Can
many small requests cause the same, especially with a slow network
connection (or it might even go down for some reason?

If I understand correctly, waiting here could cause qemu to become
unresponsive, right?

Kevin