Re: [Qemu-devel] [PATCH v2 2/2] vnc: threaded VNC server

[Avi Kivity <avi@redhat.com>]

On 06/06/2010 05:48 PM, Corentin Chary wrote:
> On Sun, Jun 6, 2010 at 4:11 PM, Avi Kivity<avi@redhat.com>  wrote:
>    
>> On 06/04/2010 04:20 PM, Corentin Chary wrote:
>>      
>>> +    if (vnc_trylock_display(vd)) {
>>> +        vd->timer_interval = VNC_REFRESH_INTERVAL_BASE;
>>> +        qemu_mod_timer(vd->timer, qemu_get_clock(rt_clock) +
>>> +                       vd->timer_interval);
>>> +        return;
>>> +    }
>>> +
>>>       has_dirty = vnc_refresh_server_surface(vd);
>>> +    vnc_unlock_display(vd);
>>>
>>>        
>> This could delay the update by quite a bit, no?
>>      
> Yep, but it's far better than waiting the lock because it doesn't slow
> down the main thread.
> I played big buck bunny trailler (33sec) in mplayer and tight encoding:
> - ~40 sec with the non-threaded server
> - ~37 sec with a lock
> - ~33 sec with a try_lock
>    

Definitely, blocking the main thread is a no-no.

>> A more elaborate approach would be to enqueue the refresh job into the
>> queue.  May need the iothread enabled so we have qemu_mutex.
>>      
> Maybe, but I'd like to wait the generic async work subsystem before
> adding different kind of jobs to the queue. And it's already a big
> improvment over the current code :).
>    

Hm, ok.

>> btw, I could not find other uses of vd->mutex, shouldn't it protect against
>> the work thread?
>>      
> Check vnc-jobs.c, there is a qemu_mutex_lock(vs->vd->mutex);
>
>    

Shouldn't it use vnc_lock_display()?  That's why I missed it.

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